Nineteenth-century material continues to be strong, and great pieces continue to be very hard to come by and are actively fought over. The upper end of this market never seems to miss a beat. Rarity does assure that prices rarely fall in this area, and more and more collectors moving into this area have fed demand. A few elements of this part of the market look a little overpriced at this stage (Le Gray, Cravens) due to some heavy run-up at the auctions by Sheik Al Thani and others. While other parts still look distinctly underpriced (Talbot and other British and most French calotypists come to mind), largely due to the fact that little important work in these areas have come to auction recently due to its rarity. You might also add important American salt prints to this hit list, if you can find any at all on the market.
Because there is so little of quality becoming available and poorer images in poorer conditions are the usual fare, extreme price spikes are to be expected at auction when unique prime 19th century pieces appear. The Jammes sale was not the only sale to see huge price jumps for a given photographer's work. Auctions are generally a poor place to buy such work if economic considerations are a factor in your decision-making, but they may be the only place to buy certain images. However, your strategy should be to try to find the rarer work in good to mint condition and buy it privately from dealers or other collectors.
I don't foresee any drop off in most market prices here, even if a true recession was to materialize at some point. It still looks like a reasonable and disciplined market to me. The only drawback may be for buyers: slower economies sometimes encourage consignors to hold on to their items, even though there may not be any rational (or historical) reasons for this.
Daguerreotypes of quality have had a very good run-up as of late. The Sotheby's Feigenbaum sale of Southworth & Hawes material certainly opened up this market to a lot of new buyers and at levels rarely seen prior to the sale. While it didn't necessarily boost the prices of other dags, the sale did build a bigger, stronger, more liquid market, as has eBay on the lower end of the daguerreotype scale.
The lower and mid-priced part of the 19th century photography market has always been more susceptible to market fluctuations and individual quirks. Graham Nash's recent purchases on eBay in daguerreotypes have, for instance, breathed a little extra life into that area. Al Thani's purchases in the photographica equipment area turned the London market a little upside down for a while. And a trio of somewhat naïve (at least those known) buyers set the market for gold mining scenes on its ear. Markets tend to return to more normal levels after such individual buying drops off. Sometimes (as in the case of the gold-mining hard images) they even fall below previously established levels, albeit temporarily. I guess you might call this the pendulum factor.
This lower to mid-priced level is the part of the market that floats between photo history/photo art and hobbyist interests (I am arbitrarily defining hobbyist items as material collected for their specific subject matter). The closer the item is to pure hobbyist, the more likely it is to lose liquidity and even price in downturns. You can almost see the hobbyist market change by viewing results on eBay these days, which is surprisingly more tied to stock market variables than other areas of the photo market, perhaps because those on computer systems are more inclined to check their stocks daily.
The photo history/photo art side tends not to have price levels slip, but can lose some liquidity (in other words, the item doesn't sell as quickly, or there are higher buy-ins in this area at auction). But good, interesting pieces, even at lower price levels, will still sell well. Quality Middle Eastern, Asian and early Italian pieces have been selling at a premium in Europe compared to the U.S.A. market; although after Christie's NY sold a single Bonfils image for over $5,000 in its October sale, it is clear that the U.S. market is catching up quickly. I have also seen much more institutional interest in this work, particularly pieces with an ethnographic orientation, than previous.