The first thing I wanted to note (but got sidetracked with my own recollections) is that when one discusses "the market" it is an erroneous assumption to paint the various markets with one broad stroke.
First, you have coin shows and paper money auctions, which I would suggest is a fairly intense market since most people there are collectors or interested/invested dealers, individuals. This market is competitive & does not tolerate common notes (esp at auctions) so I would suggest that it has been slowed down much less than the world market. Also, most collectors/investors have seen dips in markets before, know things are slow now, so they would (rightfully) believe this is an opportunity to buy. If I had the time/resources, I would be focussed on this market.
Second, you have a world real market in coin shops coin shows (bourses) around the world. While the bourses at shows may remain stable (for the next few years at least) the actual real world shops seem to be in decline due to the virtual (3rd) market. These markets typically seek considerable mark-ups in price (close to book) and most dealers would expect a little bit of haggling/dealing when selling. Although we may see far fewer "brick'n'mortar" shops, we might stop to think how few there were before the heady days 2000- 2008, and their decline may just be the result of a market correction (combined with the low overhead of online business). Still, most serious collectors prefer the 1st and 2nd real markets simply because they can inspect the note they wish to purchase (however, they don't totally avoid the 3rd market for graded notes, or a find they know they can bank on!)
The last (virtual market) is obviously notes bought/sold online (ebay, ebid, and some e-dealers). I believe it is these virtual markets where we've seen the greatest slow down but that may also be due to the fact that most people in the business know that there is stifled interest and they're dumping the "Garden variety" chaff which really should go back to banks (rather then be sold for a mark up). Insert & special number hunters will never do this (return their finds to a bank) so you have a huge glut when it comes to most recent issues. There are many e-dealers who list their notes as if everyone were as plush as the heady days. I believe the boomers are also flooding online auction sites with stashes left to them in safety deposit boxes (54- Bird series: which only confuses the true state of the virtual market!) That stuff sold when there was greater interests in notes (when the general world economy was much healthier) but those times have past. We've also see some crazy activity on many of these online sites where polymer notes are selling for a 15 - 30% mark up when they can be withdrawn from your branch at the bank. Considering all the "Buy it now" and pie in the sky "Best offer" listings of desirable notes, it is no small wonder that notes listed as true auction style listings can do fairly well (provided they're actually a note worthy of interest).
Finally, I wouldn't feel any compulsion to go out and sell my collection over night. True, the US, Europe and world economy is in turmoil right now. However, things usually recover though this slump may be long. Canada has weathered the storm fairly well (look how Mark Carney has been offered a job in England). After Australia went polymer their regular replacement notes shot up considerably. If history is any indicator there could be similar trends seen here. The one undeniable fact is: all three markets are fluid and typically experience ups and downs (with interest varying on different types of notes). I may be an optimist, but I still happen to believe that the upcoming $20.00 , $10.00 , and $5.00 polymer editions will likely spark some interest in paper as they're released. While it may be true that Gen Y collectors are few and far between, their numbers still could grow, as could the gender imbalance improve. Time will only tell.