A few points to consider:

* HG craps on IG. Definitely a worthwhile upgrade, even if you're friction shifting.
* Pff, your old 600 hub is 'obsolete'. It's a lovely bit of work, and easily upgradeable with a second-hand part you can find for nothing.
* Whether you should upgrade to an 8/9/10spd cassette body or a 7spd HG one depends on whether you really, really want another gear or not; 8spd doesn't wear significantly faster than 7spd (although 9 & 10spd do), but the longer cassette body makes for a weaker wheel for a given OLD, and the shorter cable pull per shift is less reliable and more finnicky.
* If you had a 126mm OLD aluminium frame you couldn't spread and wanted a wider cassette body, this isn't recommended, particularly if you're heavy - but it's perfectly fine if you use an off-centre rim.
* The 5mm spacing of Shimano 7spd is identical to Campy's 8spd spacing, so old 8spd Ergos and RD will work. These are generally more reliable than STIs; easily rebuildable and all that usually happens with them is you need to tweak a bit of tension back into the indexing springs. The best front shifting of any brifter, and it'll work a triple. Remaining with 7spd will avoid the need for a re-dish and maybe a new axle, not that that's a big deal.
* Jtek's various models of Shiftmate allow you to mix and match shifter/derailleur/cassette brands and speeds to a large extent.

Hey, you have tubulars on that baby? Cool!

I heard the go is to throw a little Stan's sealant (for tubeless tyres) in there; I've been thinking about building up myself another set of singles ever since...