Mine for my wife's visas were two and half pages and then half a page for the index.
Quite a few people out there have had copies of them to give them an idea of what to write but I agree with you. Keep it as brief as possible and also keep the emotional stuff of of it too as far as possible.
A couple of letters I edited for people were double the length they needed to be. Full of how much they love each other, soulmates etc etc.