The cams are good but at £800+ it does get expensive!
You could whack a charger in there but most of the work would be planning on where to fit it! Exhaust wise, You've done the main jobs, maybe a stainless downpipe and manifold, Lightened flywheel isn't too expensive too, Q2 is a must if you haven't already, or if you're feeling exotic, you could try and source a complete GTA engine from a scrapper for about £2k minimum! Although the sound on the Busso is amazing, it's not the cheapest engine to tune, and the other problem is, there's not many companies that source such tuneable parts, Alfa always get left in the dark and leave it to the people that like tinkering as a hobby, To which this forum will account for 95% of those people!
You've just been done by a Twinny!