One thing I think we can all agree on is that, even if we don't sign anyone, the collective sum of the team will be higher than the value of the individual parts. In the sense that the team will have the confidence and more experience of playing together. It's what's kept United on our tails this season. Without it they'd have been 10 points off I'm certain of it.
Also, if indeed Tevez has said he'll behave until his contract has run out, then we have such a powerful asset in addition to our squad. I think he and Yaya Toure are the only two who really have everything necessary to take a game by the scruff of the neck and slam dunk it. Not a criticism of other players, because they all play vital roles in their positions, but the two mentioned really have the rare talent of being able to "dictate games".
I am of the opinion however that we could do with two players.
1) Another attacking midfielder. This will allow us to play 2 of either Nasri, Silva, or X, while resting the other. It was clear Silva needed resting and was carrying a heavy burden of creativity especially around Feb/Mar/Apr. He also complained of carrying a knock but played through it (what a beast by the way). With that sort of rotation policy it would minimise those problems.
2) Ideally another Yaya. It seems players like Yaya are few and far between, and the ones we know of are getting on (eg. De Rossi). I personally haven't seen enough of Martinez to comment, but if what I read is true then it's the sort of player we need. We need someone with the defensive capabilities of De Jong, but the forward thinking passing of Barry. If Martinez can do that then we should be looking at him. Especially as he has proven to be able to cover centre back. That "two bird one stone" factor is something we know Mancini likes.
If our summer ended with the addition of two players of the style mentioned. I'd be happy, but I'm certainly not panicking (yet. haha). There is a lot of talk about new strikers but to be honest, I'm very happy with to keep the strike force we have. There are certainly better options than Balotelli (attitude) and Dzeko (confidence), but you can't have it all.