I'm unsure I'd have the ability to track down the owner of the car that was next to mine and who may not have been responsible for damage anyway and insist on looking at their car to see if there is any evidence. It all sounds a bit far-fetched to me. If the store CCTV doesn't show anything, and one would only ask for major damage anyway, what's the point ? Less stressful to swear like a trooper and just get it fixed. And maybe hope karma is a real thing.
No, I try not to straddle any lines even if it means getting back in and adjusting the position. I've accidentally been on one once or twice but usually because the car next to me is too far over anyway. There should be a legal minimum width for such bays.