I have it too, only one knee, and it won't go away. Stretching seems to help general knee comfort, i.e. the ability of the joint to put up with the bursitis without it causing ITBS or other pain, but doesn't make the bursitis go away. My hams are more flexible that most folks my age, i.e. I just now stood up from the computer and put my knuckles on the floor while wearing thick soled shoes.

OTOH, it only starts to affect my cycling when I go over 70 miles of hard riding and I seem to be able to hike for however long. So I guess it's under control, sort of. Bummer that it hurts, though. My guess is that I injured a tendon attachment somehow and the resultant swelling is causing the bursitis. In which case it should go away after about 6 months.

Messing with saddle height didn't help. Messing with pedal stroke mechanics didn't help. NSAIDs help a little, but less than I expected.

So I'd say stretch for general comfort because that helped my problem and it probably won't hurt you.