I'd never noticed any difference in treatment previously, but on my flight from LHR-LAX yesterday I got slightly lesser treatment as an SWU-upgraded business class passenger. The FA came by to take meal orders and I chose chicken, of which there was one left. He then went to the next passenger, who also wanted chicken, so he went back to me and said that "since [I'd] been upgraded, would you mind taking steak instead?"

Not that big of a deal, and I was mostly just happy to not be flying coach, but it looks like in certain cases AA does give preferential treatment to paid passengers.