The only way to avoid scratches is to treat your bike like a piece of pretty artwork and hang it on the wall, never to be ridden. What's the point in that? If a bicycle is used the way it was meant to be used then scratces are unavoidable.
RE: kickstands. I love 'em!! They are especially useful in large organized events. When there are already 300 bicycles at the quiky-mart it can be really hard to find a leaning space. A kick stand solves the problem.
Bike snobs laugh but I don't care.
RE: chainstay failure. I never thought of that. I have had a kickstand on my aluminum hybrid for over year with no problems. Is it only a problem on certain (thin) aluminum frames or with all of them?