In your situation I would stay given that TATL upgrades are a priority, plus add on the lounge access and priority boarding. The program should work for you.
In my own situation, I am unlikely to get to 50k miles next year in any case, but will probably get over 35K, but most of my miles will be on UA with a few AC domestic. For TATL, I want as close to a guarantee of a J seat as I can get, which means the upgrade program as it currently operates is no good for me (especially now that the London/Europe Pass is so much more expensive). I'm switching to UA's program because I'll get E+. The lounges I can live without, so I'm ok there.