I think our build up play is good when our creative players, Arteta in particular, are in form. I agree about our lack of pace, Moyes has had long enough to bring a wide player in who has the legs to join in and make the formation more expansive.
I disagree on Cahill, I think there was a time when Tim was a 'midfielder', but times have changed and his role is completely different now. If you compare him to Lampard, for example, or Gerrard to a lesser extent, he does nowhere near the amount of duties in midfield areas, in terms of creativity and defending.
His pressing and chasing is either done on the centre backs or whoever the deep lying midfielder is. If we are being pinned back then he might drop in and make it a five, but that is very rare nowadays. This isn't a criticism of Cahill, he's doing really well to be fair to him, but that's his style.
If you look at teams who play similar formations to us, they all do the same thing. Manchester Utd, for example, might be 4-4-2 on paper, but Rooney and Berbatov are constantly dropping off and dropping into midfield. Ferguson has actually claimed he's never used 4-4-2 in all his career, which was quite interesting.
I think the key to this is introducing different players and making the formation we play as expansive as possible. A pacy wide player is needed, I wouldn't be against introducing Rodwell either, but he's far more athletic than the rest of our midfielders. Obviously we won't solve all our problems with the current squad, but it can be improved on, and the formation really isn't the problem.