Whilst £12m is hard cash it's always incredibly hard to equate it to value when you you take in to account all the factors of a signing (need, other clubs, players age, position they play, blah blah). Is he a 5th as good as Torres? At the moment yes, is he a 3rd as good as Carroll, probably yes. Is he more than twice as good as Berbatov? No.
I think we should enjoy him whilst he's here as I don't think it will be forever.