Indeed, Hamsik would be great, but so would Aquilani, I mean, next summer, we'll have to choose, Aquilani or another option.
If Aquilani keeps performing, I don't see the need to invest in two CM's, unless one of the other 3 leave (counting Marchisio in).
And then still, the most likely one would be Sissoko, I don't see us getting enough money to go for Hamsik considering we will also get at least one striker and one or two defenders.
Money doesn't grow on trees, at least, not in Belgium.