Use this procedure. It has always worked for me, and I am sure it will work for you.
Wet sand with
3m 1500 grit until the yellowing and roughness is gone.
If it is really bad, I might break out the 1000, but must be very careful with it.
Follow up wet sanding with 2000 grit.
Use an old pad on a rotary, and Turtle wax *polishing* compound. Worked a few passes in with that on speed 2.5-3.0
After you have gained most of the clarity back, on a different pad, use
Meguiars Plastix for a few passes on speed 3-3.5
It normally takes around 45mins. per lens when wet sanding. Polishing steps usually take 20 minutes per lens. So all in all, you are looking at about 2-3 hours for a pair.
BEFORE
AFTER MY PROCESS
Not 100% perfect, but they look really dang good.