I am not sure that I fit into the football fan category. My leanings are towards Man City because traditionally my family supported them. However in the 60s and 70s when it was possible to just turn up and watch a game. I tended to see more United games than City's. Mainly because all my mates were United supporters.
I am not a die hard City fan, I will always support any Northern team against a Southern team. I feel slightly uncomfortable about City "Buying" success, but that's life. They aren't the first team to do that, and they won't be the last. I happen to believe that when Sir Alex goes, United will collapse for a time. We saw it happen with Liverpool who ruled the roost for years.
However these things tend to go in circles. Motivation is not about money. It takes a special talent to motivate a young man who is earning more in a week, than most of us could dream of earning in 20 plus years. I don't particularly care who wins. I will probably get slated for saying this, but in my humble opinion, the very highly paid Wayne Rooney gives 100% effort when he is playing. There are lots of other players, who seem happy to turn up and collect their pay. Their loyalty, (and their agents) seems to be to their next pay cheque. I would argue that whether any sports star is worth the money they are paid nowadays, but that's another story.