It's possible that using high quality templates in your project to give it visual interest might make your project more "engaging" for your stakeholders, giving you a competitive advantage. Templates can raise the perceived professionalism of your project: The same way that a suit might make you appear more professional when going on a job interview, the use of project templates can make your project appear more professional.
You may even find a form that has already been completely filled out that will allow you to see exactly how a successful proposal should be written. In most cases the forms will include spaces for you to add pictures, charts and graphs as necessary to explain your proposal in such a manner that makes it much easier for the reader to understand your proposal. In many cases the more detail used to explain a proposal, the better the odds are that you are going to be submitting the winning bid.