There is! Many M42 lenses are going for twice what they were only a year or two ago. Many of the Contax/Yashica mount manual focus SLR lenses are WAY up vs. 2-3 years ago for this exact reason especially the wides as Canon DSLR shooters like them better vs some of the Canon offerings. Glad I loaded myself up for my RTSII and RX a few years ago before the prices mostly rose. Seems to be a new resurgance lately I think a lot because of the Sony NEX cameras and the cheap adapters from China.
It's because of videographers as well - they love manual lenses for the 'filmic' look they give, and manual focus lenses are better, as in no focussing noise etc.
Mamiya 645 Super | Nikon F4/F100 | Minolta Maxxum 9/Dynax 7/X-700/X-500/XD7/SRT-101 | Pentax Spotmatic | Canonet QL 19 (GII) | and a whole bunch of glass