Just to put in my two cents...(don't know how similar the Elite loads are to EWR, but anyway..)

I fly to Vegas two or three times/yr. out of IAH. Almost always leave on a Tuesday afternoon and come back on Saturday afternoon/evening. I've never been upgraded on the Tuesday afternoon flight, but always get the EUA 24 hrs. out on the Saturday return. As a friend of mine says, "Who the heck leaves Vegas on a Saturday??" That's probably why I never have a problem getting the EUA.

IMHO, the closer you get to the weekend, the harder it is to get an upgrade, so Wednesday afternoons would be even tougher than Tuesdays. I've been upgraded every time I take the first flight out in the morning on a Tuesday, but the afternoon flights allow for connecting passengers (including a lot of Elites who outrank me) to fill up the FC cabin. As a Silver, I'm fairly pleased with my EUA % overall on my Vegas trips. Golds should obviously do even better...... and I'll be Gold next month, so we'll see !