"I could exit over Sheppards Pass and maybe visit Center Basin??? Then shuttle back to Onion Valley."
A nice route, and the easiest way to do Shepherd Pass. Perhaps a bit more straightforward would be to visit Center Basin before going over Forester Pass, then make a beeline for Shepherd Pass. A nice little side trip would be to leave the Shepherd Pass trail just before you get to the pass and head south up a gradual slope a quarter mile or so to a saddle at ~12,400', just below Mt Tyndall. From there you can take a peek at the awesome East Face of Mt Tyndall and have a full on view of Mt Williamson and Williamson Bowl. You can't go any further legally during September because it is a Bighorn Sheep reserve and is closed to hiking then. It is a neat area seldom visited except by stealth climbers. A note on Center Basin: several years ago it was closed to camping due to bear problems. You might want to check with the rangers to get the latest beta on that situation.
"Or after crossing Forrester head over to Lake South America and either cross Milly Foot Pass, Lucys Footpath or Harrison Pass. I have heard that Millys and Lucys are pretty difficult class 2. Harrison Pass seems a bit more straight forward."
Harrison is by far the safer of the 3 alternatives. I checked them all out years ago and decided that since they were so close together, why not take the safer route. All 3 will get you to East Lake in more or less the same time. I have crossed Harrison 4 times, south to north, in both August and September and never encountered any snow to speak of. However, this is a heavy snow year, and that definitely may not be the case this year. There are a couple of awkward moves right at the top, but from there on down it is basically a talus/boulder hopping affair. Take it slow and easy, and you shouldn't have any trouble. Another possibility is a little known pass between Lucy's and Milly's called Joe's Pass that Cola Vaughan referred to in a recent thread on crossing the Kings Kern Divide. It is reputed to be easy class 2 and basically snow free. You might want to PM him and get more details before making a final decision.
"If I were to cross Harrison it looks like I could cross country it back to Vidette, or I could head over to Lake Reflection, then to East Lake and back to Vidette Meadows."
East Lake is the long way, but all on trail from the small lake below and north of Mt Ericsson(Golden Lake? Golden Trout Lake? My memory is hazy and I don't have a map in front of me). The cross country route you mention over Deerhorn Col is one I never got around to, basically because I was fed up with Bubbs Creek, the crowds and the bears. Still, I look at it wistfully on a map from time to time. It is a very attractive route and I have some regrets. If you go that way, would you let me know what you think of it?