"As for me as the superior side, it's not bad as long as their tempo of play doesn't suddenly go way down."
Agreed.
"I don't mind playing till mate in an OTB tourney against an expert. But I may not feel like a post mortem... I may feel like they need to back to the hotel room and brush up on ladder mates before talking about anything more advanced..."
Fair enough. In my case though, I don't see myself being fatigued in such a soft position as say a queen up endgame where I can gobble up a bunch of pawns and make as many queens as I want. Would I be fatigued after winning against a non-resigner who was a piece down? Sure, but failing to win a piece up is far, far more likely than 1 in a million and it's something I have done or come close to doing a few times.
In summary, if it's a winning advantage like a piece up, I may work hard to win it but I respect my opponent's decision as his chances are not totally squandered. If it's a one in a million position like up two queens, well I'm not really suffering too much to allow my opponent to continue his hope, am I?
I enjoy it when my opponent is in a lost position but plays on anyway. It allows me to sharpen up my endgame and look for the quickest mate.