By habit due to a bit of a personal fleet building compulsion (and because I am often looking for boats for friends who we've introduced to paddling) I have tracked the kayak postings for my city, region and even some outlying areas on a near daily basis for years. (One of those areas I look at is your own, in fact, since I have been watching for a starter touring kayak for my brother in Saratoga Springs.)
Since mid-summer I too have noticed distinct lagging in the sales of ANY sort of used craft, beginning with the higher end sea kayaks though it has now progressed to even the plastic rec boats. This seems to be more pronounced than the usual end-of-season lull. Up until recently, ANY kayak that showed up on our local Craigslist never stayed posted for more than a few days, unless it had an unrealistically high price.
In fact, I listed a 15 year old Dagger touring boat in late June and got 5 calls within the first 15 minutes the post appeared, selling the boat for more than I listed it for by the end of the same day. A month later, an ad for an almost identical vintage boat languished for weeks before I dropped the price and even offered to pay the gas mileage of the guy who eventually bought it.
My instinct (developed during nearly a decade of working in the wilderness outfitting industry and 40 years of participation and teaching related activities) is that, like all outdoor adventure sports, kayaking popularity is cyclic and we are in a downward cycle at the moment. On the other hand, there seems to be a resurgence in crew and sculling among young people, at least in the inland waters.
I was struck by the scarcity of kayakers when we were out in the Pacific Northwest early last month -- when I was out there at the same time 4 years ago I spotted them everywhere. We were traveling along waterways most of the trip (the Pacific coastline, Strait of Juan de Fuca, Puget Sound and many mountain lakes) yet I can count on one hand the kayakers we saw, despite fantastic weather and mostly calm waters. I have seen kayaks posted on Ebay with no minimum languishing with no bids and some posted with bargain "buy now" prices that expired with no purchase (been tempted myself but am trying to retire by next summer and thus enforcing personal restraint.)
I'll be interested to hear what others are noticing about this.
On the other hand, sales of used canoes seem to be more vigorous, at least here in the northern Appalachian region.