Ally, I've actually only done 1 "performance" rebuild, but a fair few others, that said I have learnt loads in the past year...
Short answer, lighten/balance, port/polish yes, long answer follows:
I hadn't really attached much significance to balancing and lightening as they have the be pretty well balanced before they leave the factory and the ports have got to be good before leaving the factory, after all the guys at Alfa have been doing this for a while, right? NO, very wrong, having the bottom end balanced makes a huge difference and a basic balance is actually pretty cheap (~£100), a bit more when you start to lighten stuff, and as for porting and polishing, again, mass production takes it's toll and big improvements can be had for not to much effort.
My engine (now 2.0) has been lightened/balanced and ported/polished but is still running standard 1.8 cams and map but was comparable to a well sorted 2.0 with squadra and other stuff. Still to fit big cams and chip
Engine is soooo sweet, free revving and takes off like a shot when it hits 3k, last thing, throw away the balance shafts & get a couple of plugs spun up
a far easier way to do it than what I did!