I personally don't think i would have made a huge amount of difference. He was bowling pretty well before he got injured.
I think its especially true if Tremlett had been brought in for Finn at Melbourne, considering we lost at Perth even when Tremmers was bowling well. He certainly could have done just as good a job as Bresnan did imo.
Edit: And he's nothing like Mitchell Johnson, much more consistently accurate bowler. Especially now.