Here's my 2p's worth:
The pininfarina styling is great, though the designers had to make some comprimises in the styling to retain practicality - mainly the front bumper, it should come down a few centimetres lower so that it follows the line of the side skirts, but they made it as is so that it wouldn't hit curbs etc. - so I think that the Novitec or JMS front splitter does a great job of subtly improving the car's lines.
Hopefully I'll be adding one of them in the future, (specially as they're both quiet cheap), which will complete mine as I've got a low key quad exhaust and is lowered on eibach springs. + maybe some good 18s when the tyres need changing..
The Cup kit is nice, somtimes I think it's slightly ott, but I'd have it over the standard everytime.
Lester and Cadumaro are just far to extreme and don't do the car any favours - except make it individual.
Luke's Proteo red GTV was a great example, but I personally don't rate the Autodelta front splitter at all.
Have seen one with the AD skirts and Novitec front and they went great together.
Not sure if these links will work for everyone, but are the two of the best around:
SportsAlfa.com :: View topic - Alfa and Omega