Great answer mdfriend!
I'd add one other nice thing you can do for your neighbors: If their crop on Cletus's Farm has rotted/wilted, you can tap it and restore it for them, so they have another chance at the payout. This doesn't happen a lot with active players, but I come across it every now and then.
My other comment/question is about multiple entries/exits in friends' Springfields to drive up your bonus percentage for tapping. I've seen a few people suggest that this can cause the friend's Springfield to crash, but it's not at all clear to me whether this is based on empirical observation, or at least solid knowledge of software/hardware issues... or is this just a theory developed by people who are aesthetically unhappy with the "friends trick" and would like to ascribe negative consequences to it?