Mirrorless cameras can easily be adapted to work with virtually any lens, although most often this will be in the manual focus mode and there will be no electronic connection between lens and camera, so you have to select the f/stop on your lens.
However with the modes for manual focus like zoomed in focus and focus peaking, using a manual focus lens is actually easier with a mirrorless camera than with a DSLR...
This has resulted in the upsurge in popularity of "vintage lenses" especially those with an M-42 mounts.
While manual focus lenses are quite nice for a lot of video work, I personally would not use an M-42 manual focus/exposure lens for anything but special effects in stills.
The lens which certainly has special effects that cannot be duplicated in Photoshop is the Russian Helios 58mm f/2 which when shot wide open produces a swirly bokeh which photographers either love or hate. I personally think that this swirly bokeh is pretty cool for people and just might be really nice for pictures of my white fluffy dogs.
The 58mm lens on a 1.5x crop camera produces an 87mm effective focal length which is pretty nice for head and shoulders portraits while the f/2 aperture of that lens allows shooting head and shoulders portraits with really narrow DOF increasing the swirly bokeh rendition.
Another series of lenses which are becoming popular are the "Bubble Bokeh" lenses from Fujinon and other manufacturers such as Pentacon.
It would be fun to just play with some of these lenses and despite the fact that their prices are going up, they still wouldn't break the bank to own one or even a couple...
I remember when you could hardly give away lenses like the screw mount Pentax Takumar's but, these lenses along with the Russian Helios are gaining in popularity along with a surge in prices.