It seems to me like having a screen protector should be the best case. Isn't this the sort of thing they are for? Peal it off and stick a new one on; much easier than scrubbing down your screen.
Possibly. In my experience, screen protectors are fiddly to put on, and when I had one I never wanted to have to replace it. Far too easy to get bubbles. There's also some amount of cost involved in replacing it, no matter how small. Rubbing alcohol is just something you typically have lying around your house, the marginal cost is less than a penny. A quick wipe with an alcohol-moistened tissue is all it takes.
Hmm. Maybe they should make screen protectors with built in screen protector protectors. Each time something gets messed up you just peal off one of the several layers, like some sort of flaky biscuit of screen protection. :)