I don't think it is unreasonable at all. I've got a 14 year old 4Runner with 160k+ miles and I still park as far away from everyone as I possibly can. Yes I have plenty of pinstriping from trees and such when off roading, but those were caused by me using what the car was made for. They weren't caused by some ungrateful uncaring idiot who threw their door into me. I've never thrown my door into another car so it isn't something that is hard to do. People are just stupid and can't seem to figure out why they should car about your things when they don't have nice things, or don't car about their things.
As for avoiding dings I park as far away as I can, always try and park at the end of a row by one of those median/flower bed things and park as close to the curb side as I can to allow as much room as I can for the other spot. I also usually tend to back into parking spots when I can. It is easier for me to pull out forwards, and I seem to think that when someone backs into a spot they care more about their car then someone who pulls in regularly and maybe others will notice.
People think I'm anal with how I park my 4Runner, but I'm even worse with how I park my 87 Supra. It's in pristine condition for it's age and I'm not gonna let someone else ruin that for me. Neither of them are worth a whole lot, but they're mine and I'm proud of them. Sorry about the long post, but this is something that seriously irks me.