Without spending a bit, you're unlikely to get the same performance as some of the Jap machines from the same era and even then maybe not quite to that level. And what you have to spend to get that performance may be far more than the bike is worth.
Having sad that, you are obviously mad because you are a Benelli owner and none of what I said makes a difference anyway. Get your wallet out:
I asked Facciolo how much to do everything, the whole lot, it's €10k. I'm saving in between racing
If you're not aiming quite that high, the biggest gains are going to be getting it ported and a set of expansion pipes. Make sure the internals are up to the job though.