Hmmm. I'd say the 20K miles is definitely worth it just for EWR-GLA, especially if it's on a 757, you don't want to be in coach.
You'll have to chance it on the SFO-EWR leg, but usually mileage upgrades are at the top of the waitlist. This is a tough route, though, lots of paid F, though I doubt anybody pays full Y and gets free elite upgrade since they have non-Y fully refundable tickets for much cheaper.

I would check the availability periodically (you can use http://flyaow.com/classamex.htm) and keep an eye out for inventory in "F" class. As soon as you see the number next to "F" >0, call up CO and make sure they clear you into First. Their computers aren't always so swift.

Good luck.