I think Robbie has a good point. As bike manufacturers re-intorduce steel to their line-up, old steel will lose some demand. It all depends on what the new bikes sell for. If I were to look at the C&V as an investment, the bikes that will increase the most by percentage are the ones that have not yet taken off. Nishiki, Univega, Centurion LeMans, Schwinns and so on, will increase more as a percent of their current value.
But there's nothing like finding a $20 Bridgestone or Panasonic at a garage sale.