I technically am right now working the quads/hams three days a week through direct leg work, plyometrics, and yoga. it's great. the best part is, that each of these in succession cancel out the soreness of the one before.
don't know if that made sense, but basically, i do the plyometrics. the legs get sore. then, the yoga comes in and eases the soreness. by the time i am ready to hit the legs up directly, they are 100% again. the day after all that, i hit up some major stretching of them with some major protein consumed while i stretch for a while.
i prophecy that this'll be good! first week, so who knows. but it's been good this week. don't see why it'll change. especially as i get stronger at them.
but as far as hitting up squats/hams twice a week with conventional methods, i'd done that for a short while with success. the key is not to stack on too many reps either time, obviously.
i'd done something like this (excluding all other workouts, just showing legs):
THU: (10 reps each LIGHT LIGHT weight. first week i did 135 for squats and 185 for deads just to start, adding on weight later as i saw fit)
8 sets squats
8 sets deadlifts
4 sets ham curls
SAT: (6 reps each heavy)
4 sets squats
4 sets SL deads
hypertrophy/strength, mayn. i liked it, and will likely use something similar again someday. hope this helped.