I'm in a bit of a dilemma too with spd. I'm currently recovering from a muscle strain in the quads. However, before that happened I was looking to move from flats to spd in a hope that they would assist with achieving a better pedal stroke (not that I know there's anything wrong with it). But reading all about knee injuries just puts me right off going clipless.
I've already lost a tooth from a fall, and have had too many issues with spd (and with even toe clips after I abandoned spd) that I'm returning to flats. I think if I was riding on the road and not expecting to stop, it would be more bearable, but from leaving the home, I need to stop at junctions, crossings and a whole host of unpredictable hazards that seem to make it not much fun to go anywhere, I've gone back to flat pedals and it's easy, and the anxiety has gone. No more panics, falls or anything, except an occasional whack to the shin which is much more bearable than an emergency dentist appointment!
The real problem is the increasing anxiety that comes with using them, given the bad time I've had with them so far, I've worked myself up to panic level with them, so it undermines my confidence to even ride anywhere with them.