So I've got an early 90's Athena wheelset, Athena hubs and Campagnolo Ypsilon rims. I think the back wheel needs to be rebuilt soon, rim seems to be warped more than a true can fix, but thats besides the point really.
I've had people tell me I might as well just upgrade the whole wheelset while I'm at it. I dont have any interest in going over 7-speeds on this bike, don't care to spend that kind of money right now and to be honest I would like to do my first wheel build anyways. So the question is, whats the real advantage, if any, of upgrading my wheels in this case? How much weight do I really stand to lose?

Unless you want to go over 7spd or your a heavier rider I see no reason to switch. FW type hubs have served very well for years and the system works OK.

To us C&V riders who use 7spd setups the the only real advantage to a cassette is simply that the hub bearings are closer to the end of the axle making a stronger hub and making a bent or broken axle les likely. Shifting may be inproved slightly due to the ranps on a shimano cassette, but if your current setup is using Synchro with a Regina or Suntour FW you'll have to start hunting the correct insert to go with your new hub.

No reason unless you want more gears.

I will say this Some hubs can have the freehub swapped to make it able to run the 8 and 9 speed. The Shimano stuff this is a VERY easy swap. The one set of campy wheels I have looks like it would be a easy swap as well but my wheels are a little newer then yours. My wheelset comes set up where you cane set it up for Campy cassettes or swap the freehub to run the Shimano cassettes.

Does your freewheel still have lots of life? Probably so. Or it can be serviced to bring it back to great health and good riding.

If you like what you have and can fix the current issues, why get into the the whole dog chasing its tail routine of changing one component, which means another needs to be changed, and another, and another, etc. Trust me, I've been there.

I would do a down and dirty rebuild, find a new rim with identical erd and buy new nipples.

I can't think of a good reason to change unless the freewheel is worn out bad then it may be cheaper to rebuild the wheel with a cassette.

Shifting is so much better with a newer cassette, even in friction mode. The fun starts at 8 speeds and at 10 you can breath on the lever for a shift in friction mode. 8/9/10 cassette hubs are common and easy to come by not to mention lighter.

+1

I guess I'm in the camp that thinks cassette hubs are nicer in almost every way (minus compatibility). Not to mention that equivalent high end hubs today are leagues ahead of older hubs. Hell, it pains me to throw away a freewheel because of all the metal it holds.

Freewheels are good enough, but are not better.

*preparing self for the lynch mob*

You can buy a modern shimano 7 spp freewheel that is gear cut like modern cassettes, spaced at 5.0 and indexes with Campy eight speed. No reason to kill all the old stuff if bargains are to be found.

Cassettes and freehubs usually have a "tighter" action. Freewheels generally have and develop play faster. They are also harder to rebuild.

I'm looking forward to running a set of open pros/ultegra wheelset I just bought.

Thanks everyone,
Freewheel seems to be in a pretty good condition as far as the life of the cogs/teeth and I've cleaned it up as much as much as possible short of disassembling and it spins/clicks great. Like I said, I dont want to go higher than 7-speed on this so I think I'll just do the rebuild. And I'm not very heavy but the weight bearing will be a good thing to keep in mind for a planned tourer.