I don't know about eBay overall, but from what I've seen the average selling price on vintage TV sets has risen quite a bit over the last few years. Many that had been selling in the $100 range have been going in the $300-$500 range.
Check out this thread for examples:
http://www.videokarma.org/showthread.php?t=247500
I think the point others were making is that not all sets are created equal. For example, check this out:
http://www.tvhistory.tv/1947-53-USA-...Production.JPG
About 170,000 sets in 1947, almost 7,500,000 in 1950. Also the earlier sets had more unique designs, features etc. That's why generally post 1950 sets are worth far less with the exception of early color sets and the Philco Predictas. Will that change in the future ? Dunno, but for now they just don't sell for much.
Personally, I don't pay much attention to the price. If I like it and can afford it, I'll pick it up
