If you need 2 suitcases at 70lb each, then fo is worth it. Otherwise, if you have a delta Amex gold or plat or reserve, the benefits of fo aren't much more.
Upgrades vary, but from cvg, jfk, fll, dtw, and ewr, I got upgraded always even when I was fo. My last flight from dtw-lga didn't get ug even though im a gm now. So it really depends on ur routs and times.
But if u always travel with ur gm partner, then there's really not much benefit being fo (a little, like 25% extra miles and irrop, but not much)