One of the most persistent traits I have observed in charities that are going broke is a certain steadfast focus on what I like to call "inappropriate perfectionism." I suppose that sort of perfection would work in fields where you have unlimited time to complete a task. In grant writing, however, we are restricted by deadlines.
General Colin Powell, for example, teaches that military leaders need to take action even if they only have 80% of the information they need to make a decision. The problem, as he sees it, is that if they wait for the other 20% they will be in danger of losing the opportunity before them.
In a similar way, I think it is a mistake to try to obtain anything like 100% perfection in your grant applications. This level of perfectionism takes up too much time that might be applied - more profitably - to other worthwhile objectives, including applying to other funders for grants.
In my experience, I really don't gain all that much more from the funder with that extra 20% of perfection I've built into my grant application. As long as I have all the elements that the funders are requesting in their application guidelines, then I'm typically better off spending my time writing some additional new grant applications.
One problem with setting 100% perfection as your standard is that you become tempted to simply recycle existing, already perfected material. Although this seems like a smart idea on the surface, in my experience it leaves you with a grant that often displays little attention to the articulated needs of the funder. You have, in a sense, given them the perfect answer for someone else's grant application.
The folks that read grant applications for a living seem to develop an odd sixth sense that lets them know when an old grant has simply been recycled for a new audience. They can detect recycling through the consistency of your message and the way you highlight (or de-emphasize) key elements of your proposal.