Implementing a 6-phase approach to Marketing Plan Development could help alleviate the current issues:

1. Situational Analysis: Understand the business context, customer segments, and market trends. Identify inefficiencies in existing marketing plans.
2. Goal Setting: Align marketing objectives with business objectives. Ensure these goals are Specific, Measurable, Attainable, Relevant, and Timely (SMART).
3. Strategy Formulation: Develop a comprehensive, detailed marketing strategy - considering segmentation, targeting, positioning, and differentiation approaches.
4. Tactic Development: Determine the specific actions required to implement the strategy, from media planning and content production to customer engagement tactics.
5. Action Plan and Budgeting: Establish a clear action plan, allocate responsibilities, and create a detailed marketing budget.
6. Measurement and Control: Define performance metrics and Key Performance Indicators (KPIs), set up a robust performance tracking system, review and refine continually.

Company leaders could be concerned about the feasibility and scalability of the 6-phase methodology. However, this approach is designed to be iterative and scalable. It allows a proactive response to evolving market trends and fosters continual refinement and optimization. The process also ties in neatly with Agile and Lean methodologies, thus aligning well with a fast-growing digital platform.

Another consideration could be the cost and human resource implications of this methodology. The approach does require an investment of time, capital, and human resources, but in the longer run, it stands to improve the marketing plan's effectiveness, efficiency, and the return on investment - thus, proving cost-effective.

Lastly, integrating this process with the firm’s existing systems could be challenging. The solution lies in leveraging technology and automation possibilities that minimize disruption and ease the transition. For example, modern marketing planning tools and platforms can aid in a seamless transition.

Sample Deliverables

• Marketing Plan Overview Document (MS Word)
• Marketing Strategy Map (PowerPoint)
• Performance KPI Dashboard (Excel)
• Marketing Budget (Excel)
• Marketing Calendar (Excel)

One crucial aspect of effective marketing planning is intelligently segmenting the consumer base and targeting the most profitable segments. Sophisticated segmentation using customer behavior, preferences, and real-time data analytics could significantly enhance the marketing plan's impact.

Investing in Marketing Technology (MarTech) can be transformative. Tools for data analytics, campaign management, customer relationship management (CRM), and automation can simplify and streamline the marketing plan development process. The right MarTech stack can drive marketing agility, enable better decision-making, and facilitate personalized, real-time marketing.

When addressing the issue of accelerating marketing costs in the context of the digital platform's growth, executives should consider the importance of strategic alignment and cross-functional collaboration. It's been shown that alignment across the organization contributes to market success and improved financial performance, as suggested in the McKinsey Quarterly article "The Strategic Yardstick You Can't Afford to Ignore” (October 2013). By ensuring that marketing objectives are not created in isolation but are instead fully integrated with other functional strategies—product development, sales, and customer success, inter alia—the platform can create synergies that improve both the effectiveness and efficiency of the marketing spend.

To facilitate this alignment, the marketing team must collaborate with other departments to develop a comprehensive understanding of customer needs, product feature set, and competitive landscape. As stated in "Enduring Ideas: The Seven S Framework" by McKinsey, aligning skills, strategy, and shared values plays a pivotal role in organizational cohesion. Leveraging this approach, an integrated marketing plan can better align with the holistic customer journey, optimize touchpoints for user engagement, and therefore, reduce waste in marketing expenditure by ceasing actions that do not align with the overall strategic objectives.

The role of data analytics in uncovering consumer insights should be a focal point for the digital platform's marketing strategy. In the era of big data, decision-makers should prioritize the development of predictive models that can more accurately anticipate customer behaviors and preferences. "Big data: The next frontier for innovation, competition, and productivity" by the McKinsey Global Institute (May 2011) emphasizes the significant value potential that big data can bring to businesses in various sectors, including personalization at scale.

By tapping into user data, the platform can identify behavioral patterns, preferences, and trends among its most profitable segments. The insights gleaned from this analysis enable the creation of more targeted and personalized marketing efforts that not only resonate deeply with consumers but also provide superior conversion rates. Furthermore, the efficient use of data analytics ensures a continual feedback loop, refining marketing tactics in real-time and rapidly adapting to changing user dynamics—an essential capability for a fast-growing digital platform.

For a growing digital platform, expertise in agile marketing is vital. Agile marketing, which draws from the principles of agile software development, focuses on speed, transparency, adaptability, and iterative progress with a strong emphasis on data-driven decisions, as detailed in "The dawn of marketing’s new golden age," McKinsey Quarterly (February 2015). This approach enables a marketing organization to pivot quickly in response to market feedback and emerging trends, which is particularly useful for the digital platform in question.

By adopting agile practices, the marketing team can break down their work into smaller increments, allowing for accelerated cycles of planning, executing, and reviewing. This approach not only supports rapid testing, learning, and iterating, but also ensures that marketing strategies and tactics remain relevant and effective. It enables the platform to adjust and respond to user feedback and changing market conditions in near real time, thus avoiding the lag that can occur with traditional marketing planning cycles. Executives should foster an internal culture of agility and flexibility, encouraging teams to embrace experimentation, leverage cross-functional expertise, and iterate quickly.

Executives might be concerned with how to ensure each investment in marketing yields the highest possible return, especially during periods of rapid growth. It is beneficial to focus on the concept of incremental innovation within marketing strategies. As discussed in McKinsey Quarterly's "Eight Essentials of Innovation" (April 2015), the most consistent performers developed well-defined yet flexible innovation processes that scaled across contexts and portfolios. Rather than chasing transformational innovation in marketing, the platform can implement incremental changes that optimize current campaigns and strategies, resulting in continual improvement and higher ROI.

Incremental innovation in marketing can take many forms, such as refining user personas, A/B testing campaign messages, optimizing digital touchpoints, or leveraging new, yet proven, marketing channels. Each of these improvements might be small in isolation but, collectively, they can lead to substantial enhancements in marketing performance. Additionally, by focusing on incrementally bettering the marketing processes and tactics, the platform can avoid the disruption and risk associated with implementing large-scale changes, which is particularly important for maintaining the stability needed during growth phases. Implementing these practices ensures not only an improvement in the marketing ROI but also fosters a culture of continuous learning and development that can yield long-term competitiveness for the rapidly growing digital platform.