You are building a case based on proven need and innovative solution. Do not use what I call cheerleading or boosterism language. Save this language for your cover letter or for proposals to corporations or individuals. Do not mix rationale with method. Keep your discussion of why you are doing what you propose separate from how you will be doing it.
Cover letters are like bonuses, especially if there is a proposal page limit.
Try to keep them to one page. Have a top-ranking official sign them. Use them to demonstrate institutional support. Re-emphasize the main goal of the project. The flowery language that I said didn't belong in your proposal can go here.