You do need input from those who will be involved in implementation, but that does not mean everyone of them needs to approve the final proposal copy. In fact, your best editor may be someone who does not know anything about the subject of your proposal. As the proposal writer, you are more in tune with what the funding source is looking for than is any editor. Be picky about what editorial advice you choose to follow. Miss a deadline rather than submit a poor application.
Every proposal is a form of cultivation.
Do not make a bad first impression. Last minute proposals often look like last minute proposals. Always request funding source critiques of rejected proposals. Even if a funding source is unable to provide you with a written response, they may remember that you cared enough to ask for it. Second submissions are much more likely to be funded.