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.
There is nothing, absolutely nothing, half so much worth doing, as simply messing about in boats