I don't think we
need Smeijder.
Basically this has been our formation for most of 2011 for every game in which Rooney has started (West Ham first half and City home aside)
Hernandez
Park ....... Rooney .....Valencia
Carrick ... Giggs
Evra .. Vidic .. Vidic .. Fabio
Van Der Sar
De Gea or Lindegaard come in for Van Der Sar, and obviously the wing slots will be between Nani, Park, Young and Valencia.
The reason this formation worked so well in Europe especially was that defensively it allowed Carrick to do specifically what he was good at - sitting deep and intercepting the ball. Carrick isn't a harrying player, and he isn't a tackler. Giggs playing this role (Anderson being his understudy in this system) is a harrier (not the jet) - he's got the stamina, pace and agility to cause problems for the opponents in the middle, and
more importantly, and as noted by Jonathon Wilson, it allowed Rooney to get back and make tackles in the midfield. He was the one that was putting physical pressure on the opposition in that area, which was a key part of us conceding very few goals (until the final unfortunately).
If we're looking to bring a midfielder in it will be to take over from Giggs when he retires (in 2025 or some bollocks). The ideal partner for Carrick would be someone who is capable of harrying their midfield and picking a pass upfield. They'll need a great degree of mobility and positional awareness, and I don't think Sneijder is the man for that role. Basically Darren Fletcher needs to get fit again to take on this mantle (watch as people now misconstrue this as me saying Fletcher > Sneijder).
Sneijder plays best were Rooney plays in this system, but doesn't offer the same physical presence. Even if we did get him, and wanted to play him there, we'd then need someone with more physical presence to play in the position Giggs is now (probably Fletcher if he can get fit again). That won't happen because we'd have 1 striker spot that will always go to Rooney and then 6 backups (Hernandez, Berba, Owen, Welbeck, Macheda, Diouf) - it wouldn't make sense from a squad composition perspective.
If we're signing someone for 35 odd million pounds they're going to ostensibly be playing week in week out, which is why it doesn't make sense to me to pay that much for Sneijder both from a tactical and squad composition point of view.