While I've never flown it on a Monday, the 10:00pm SFO flight has usually been a very elite-lite flight for me. A few times they have sold upgrades at the gate, too. The last one I booked was within the Silver window and my upgrade cleared immediately. I ended up doing SDC on that one, so I don't know what actually looked like at departure.

Though ATL-SFO can be a tough route in general, the late flight is certainly an easier upgrade. It may not be extremely likely that you'd clear, but I wouldn't write it off completely.

Frankly, you'll get nothing other than the snack basket on that flight, so I personally wouldn't spend the extra money + 12.5K miles on it. Usually people are asleep for most of the time in the air, so service is pretty sparse.