Pete Kohler suggested that most vintage lightweights aren't even keeping up with inflation. This is probably true, depending on how you define "most." It's not true in all cases though.
As is the case with real-estate, cars, stamps, or any other *hard* investment, the prime items have been doing nothing but going up in value for the last 10 years. There are numerous reasons for this, but the deepest trend is a steady increase in actual inflation. The core inflation number reported by our own government has been deeply flawed for many years, because food and energy are not included. This is ridiculous, since everyone has to pay directly for food and energy, and those are the two most basic costs of living that have been rising the fastest (other than the price of real-estate and the cost of rent--depending on where you live, of course).
So as essential costs rise, and the dollar erodes as we print more money (the money supply has increased enormously in the last half-decade, with consequences we can all see) all true collectibles will rise in value, as will most hard assets.
Just as a for-instance, the value of the work of the great Lombard bike-builders (bikes from the 60s through 1980, more or less), has more than doubled in the last 8 years or so. Depending, naturally, on the condition, originality, and overall appeal of the individual bike. Some values of some bikes have done better than that. Whether these values will hold is anyone's guess.
But if you collected these bikes and told your wife (or partner), that they're a good investment, you weren't lying. They aren't as easy to store as stamps (more's the pity), but the right bikes have been perfectly nice investments, that offer the added aesthetic benefit of being rideable...<g>
Someone who was very picky in the last 10 years in their collecting, and who was willing to pay the fair market price at any turn, no matter how unreasonable that price might have seemed at the time, has done very well against inflation. In fact, someone who bought only the most collectible bikes in the last 10 years will have, in general, doubled their money, or better. This is at least competitive with an average real-estate investment. Although--to be fair--the best real-estate investments have tripled, or better, since 1998.
That's on the one side. On the other side are all the perfectly lovely bikes that have not increased in value. Like a Grandis I bought not long ago. A beautiful bike in every way. In quality? Equal to the great Lombard builders, and maybe better than a couple I could name. I paid $550 for it. That bike has not kept up with inflation, but it is every bit as nice as the most expensive vintage lightweights out there.
I have a Rauler from the early 1970s I bought a few years ago. I paid $550 or so for that one too, including shipping. It's *extremely* cool, and equal to an early 70s Colnago, or better, in quality. It has lots of drilling, milling, and enamelled highlights. A very attractive bike. I doubt it would sell for any more than I paid for it, if I put it on the market now though. That's ok.
And those are probably the bikes that are most pleasing in some ways. It's nice to know you can go out there and find, without much trouble, a beautiful, refined steel race-bike with all Campagnolo parts, in perfect working order with a bit of tweeking, for 500 bucks. These bikes are on ebay all the time, and are often shown in auctions so poorly presented that the price stays down even lower than it would otherwise.
Sure, I won't deny I have a few high-zoot bikes. I enjoy them. A lot. But, somehow, it's the ones that cost very little that I look at most fondly.
Charles "too many bikes but I love 'em all" Andrews Los Angeles