Actually motor mounts (front and rear isolators) should be replaced every 20-25K. I wouldn't put that off regardless of whether or not you feel something.
I do a great deal of PM and much of what I do most folks don't. Is what I do necessary? Maybe not but it doesn't hurt. PM is a lot different that having to fix crap. I hate having to actually "work" on a motorcyle so I do preventive maintenance to prevent serious wrenching. I do some things every 5, 10, and 20K miles. I would at 40K (have) replace the front fork seals, neck bearings, swing arm bearing/bushing, motor mounts, top engine stabilizer, front & rear brake pads and rotors, primary chain, wheel bearings, clutch cable, clutch cable, clutch cable, clutch cable
, check and adjust spokes, oh and did I say clutch cable
I keep my own record of what I do every year. In Spring I review everything I've done just in case. But normally when Spring comes I don't have to do anything except kick her over...o.k. "push the button".