When I was silver last year, and flying exclusives LUT fares, I had OK upgrade success (see below). Every flight was either to ATL or out of ATL. The key is flying at the most awful times (but those are when the cheap flights are offered anyway). So, for example, was upgraded ATL-SFO-ATL as an FO (as was my non-medallion companion) flying out Friday on the last flight of the night and in on Sunday, first flight of the morning.