I have definitely noticed a change in upgrade availability since I became PM. Of 7 upgradeable flights since becoming PM, I've been upgraded on 6 of them. Last year (as a GM) I had 50% (18/36) success. Flying from TPA where there are lots of Medallions, as a GM, I only rarely got upgrades on flights between TPA and ATL. Now it appears that upgrades are going to be a lot more common.
As for better treatment by DL staff, I think it's made a bit of a difference. I do find that in general, DL staff are better than other DL carriers. I do think that some DL staff have taken it to another level due to the fact that I'm a PM. And although CRC staff are usually the best of the best when it comes to courtesy, it seems that even they've gotten better. I'm not saying that the employees are any more polite, just that they try even harder to make sure I get the best seats possible, ensuring upgrades get entered and cleared, etc.