I would definitely consider signing an older player with exceptional technique and reading of the game who never relied much on physical qualities even at his peak. Pirlo to Juve, Xabi to Bayern, Berbatov to Monaco are some of the most successful examples of players 30 making their new clubs stronger.
Alves is kind of borderline case. Certainly an excellent technician and a real fighter and winner. But his position does require a lot of stamina which is what players after 30 often lose (unless they train and live obsessively like Xavier Zanetti). I would have loved to have Cafu even in his 30's in our team. Then there is an example of Maicon, a world-class full-back at Inter who wasn't great at City, but is doing well enough back in Italy. Not sure on Alves, in truth I wouldn't be against signing him just for the winning experience – unless he demands ridiculous money.