Before the page is locked (because they debate is getting boring) I'll throw my 2 pence in.
I agree with the majority of people that its best till wait till the end of the season, see how much, then its up to Moyes to make the decision.
If he wants to sign with us and wants to play for us at the right price then I dont see why we shouldn't, gives us some more depth. He was influencial at Benfica winning the league in 2004/2005 (their 1st for 11 years) when he was 19 (only missed 5 games in the whole season). A bad injury forced him out for most of the season but came back into the squad until he wanted to move on saying "the premiership is the only place I want to play".
If the price is right and he wants to commit to the club then get him bought. We first need to find out where's his best position and get him working in the system that has changed since last season. He's started 3 (unfit and a massive game against Chelsea for his 1st game) along side Carsley, more defensively, once on the right wing and it looked like he was gonna play left wing agasint City before he taken off injured.
If Moyes moulds him right, like he did with Jags and Pienaar and what you do with every new signing, he'll be a great assest. Just look at his mate Nani at Manc Utd. Fergie paid £14 mill (I think) for him and has only played him every now and then but he's a great talent. You either pay through the nose for sheer class or you pay it for potential (which is what Manc you did for Nani and Anderson, and what Spurs did for Darren Bent)
My big conern is the agents who own half of him. The situation at Pompy was [Poor language removed] for him and for Redknapp and it was all down to his [Poor language removed] stupid Agent, the Global Sports Investment. Redknapp only found late on that if he plays him for 3 consistant games he'd have to buy him for £12 mill so he gave him up to move on. We got [Poor language removed] big time at the last minute because of that because Spain doens have the 3rd party rule so Benfica got all £14 million for him.
If he's surplus to requirments at Valencia (which it looks like he is) they should be able to let him go for a bit less. If not, see ya later and get someone else.