Well here is my thoughts on this. As for the prices being on the decline, I now that in the case of rare and ultra rare snare, once you get to a certain price point you ostracize a lot of potential buyers simply because they can't afford these drums. There are a lot of collectors out there that buy these drums as investments, but the prices can only get just so high before they have to come back down. I also thin that there are a lot of younger players that have interest in these drums but from a playing perspective. I collect a bit myself but I can say that while there are a lot of drums out there that look great they also need to sound great as well and I can't see paying $4500.00 for an ultra rare snare unless I can play it. A lot of older collectors in other areas (outside of drums) have also seen declines in prices because many of the collectors from the older generations that have driven the prices up have now passed on and the younger players and new collectors can't afford the very high prices on some of these things. Price plays an important factor.
The other half of the price problem is that the collectors who now want to cash in on their investments don't want to loose money so they sometimes ask ridiculous prices. Granted, on any given day, something is only worth as much money as someone is willing to pay for it. In many cases, the drums that are fetching top dollar are also in exceptional condition but then anyone with the same or similar drum thinks that what they have is worth that much too.
A lot of younger players have shown an interest in vintage gear but they want to play it and not buy it to stick it on a shelf and stare at. These players are often on a budget so we go back to price issue but there is definitely interest. Everyone dreams of owning a vintage Black Beauty but at the end of the day, how many people can actually afford to shell out the $2500.00 - $4500.00 that they sell for.
The other factor that plays into this is availability. This is a factor that I don't think has been addressed yet in this thread. I know that modern technology has made it much easier for drum collecting to become more international than local. Add to that the fact that there are tons of shows out there on antique restoration and resale as well folks who dumpster dive, tag sale hunt and buy storage lockers, everyone under the sun has taking to trying to find that diamond in the rough or rare item in their attic or basement that is worth money. This has made finding a lot of these uncommon and rare drums a lot easier to find. Ebay and other similar site play a huge factor in this. I have sold many vintage drums that have gone to Europe, Australia and South America but 20 - 25 years ago we were still limited to our local tag sales, thrift shops etc. so things were staying local.
Bottom line, the interest is out there but I think that if you want to see more sales then prices on many things have to remain reasonable.