Fab 51, I think alot of it is that trucks seem to be finally becoming a popular "main-stream" item. I believe for years, everyone has put all of their effort into the coupes, sedans, tri-5 chevies, not to mention the Model A, T, & B Fords.
Pick up any hot-rod or street-rod magazine, and all you see is those high-dollar Boyd and Foose type rides. As such, there really hasn't been a "niche" for the old trucks. Don't you get tired of seeing the old stuff done over again and again.
The other side of that coin is the guys that don't want anything to do with something that isn't 100% original or a 100-point restoration. You know the type, when they do look over your truck, they tend to point out everything that isn't exactly perfect or didn't come with that model.
We have been introduced in the last couple of years to a new craze known as the "rat-rod". Where it is more and more acceptable to show-up with a less than perfect trailer queen. (probably fiberglass to boot!)
I also believe the Big-3 have done us some favors by going Resto on some of their designs the last few years. I know the release of the SSR certainly didn't hurt the value of my 52. Fact is, it probably increased the general publics interest in it, as they're not very likely to plunk down 50K.
Lastly, alot of us baby-boomers are finally getting to the point where we have a little bit of disposable income to spend on the days of our youth. Yeah we may have drooled over that 32 5-window, or highboy as a kid, but we lived in the stovebolts.
Those of us that were bright enough to "pick-up" (No pun intended) one of them for little or nothing, and nurse it back to health are going to be sitting on a nice investment.