I'm pretty passionate about the whole Campy thing -- I grew up in a town with a good LBS, and drooled over all the polished aluminum Campy parts under the glass case at the register every time I went in for something else -- I couldn't afford a single part, but I wanted them all. Now, happily, I have Campy stuff, and I love it.
Of course, if I really try to be coldly objective, I think that in the abstract the choice between the two really comes down to the ergonomics, and if you're used to one and don't find the ergonomics of the other compelling, stick with what you know.
On the other hand, it sounds like you're actually building these bikes on your own, so I'll assume you do your own wrenching? The Campy components are user servicable, fully rebuildable, and parts are readily available from sources here in the US (ain't cheap, but you can get them). I've stripped (to the last part) and rebuilt every component I have (2004 Chorus) other than the BB. (BTW, they didn't need rebuilding, but I wanted to do it, so I did.) If you like working on this stuff, and you're not locked into the Shimano ergonomics, I'd think this is a great opportunity to make the switch. You won't regret it.