Campy 8-speed is an orphan that isn't being supported at all. The components, when you can find them, command collector level prices.

Putting a 9/10-speed wheel (130 mm) into your frame (126 mm) is practical even without cold setting it. You have to work a little to slip the wheel in but it's not much of a struggle. If you want to upgrade and remain with Campy, you might at well go all the way to 10-speed as Campy seems to have pretty much abandoned 9-speed also.

Centaur or Veloce would be good choices to keep the cost moderate. If you stick with downtube shifters your current fd would be fine as the front shifting is strictly friction. If you want to use Ergo brifters, either find pre-2007 ones or a new fd will probably be needed as the new "QS" brifters aren't ratcheted like their predecessors.