I think the money already splashed before he was there, then the subsequent media hoo-hah about how much money will be spent has made life much more difficult for him. The best way to build up a team, would be to build it sup slowly with a few good players each season inproving in profile and slowly bild up your squad until you can get a good team together. Doing it the superstar way straight away seems to just scare the non-superstars into not performing.
Aston Villa with MO'n in charge are doing it the right way methinks. He was buying people like Zat Knight and Ashley Young, who were half decent or raw potential. Eventually Zat became the back up as more players came along and people like Curtis Davies developed, until eventually they are in for more decent names, like sidwell, young, shorey, friedel. Look where they are now, albeit with easily the best manager outside of the top 4.
Slowly built his team up until they are with a decent shout of getting in the top 4, which means he'll be able to get even more good players who aren't #$%$ mercenaries like Robinho.
Just my 2 cents. I'm sure Man City with all that cash will eventually win the carling cup or something, top 4 finish perhaps one day, the sheer financial muscle almost guarantees it, but I bet Aston Villa do it in less time. MO'n has only been there 3 or 4 seasons and he's made them one of the better teams in the league.