Like your idea but afraid you may be on to something here about their longevity. Had a bug deflector on my previous truck and it came with several of the little self-stick buttons or whaterver you call them to keep the deflector from coming in contact with the hood. After a few month they fell off. Can't tell you how many times I replaced them even using silicone glue and they just would not stay on for more than a few months. So don't get complacent and "know" you've got them installed. Check before you set your bag down would be a good idea I think.
Thats good advice, although I think your buttons on the hood would see more abuse. The heat from the engine compartment as well as the sun beating on them combined with the deflector rubbing against them when you are racing to the beer store all contribute to their long term existence.
Prepping the surface, as 103tHunDer mentions, is a critical part to them staying on.
JD