I've never been to Mammoth and I'm thinking of going Thanksgiving weekend. Has anyone ever gone at that time? Is it really crowded? As a low intermediate, would any of the greens and easy blues trails be open?
You would want Canyon Lodge to be open, otherwise you will be limited to the two bunny runs on Discovery chair and a few mainstream blue runs that will be congested with faster traffic.
Canyon has been open at Thanksgiving only 2 of the past 11 seasons, and I think that's representative of long term average.
Nobody should advance commit $$$ to Thanksgiving skiing. You have to wait until you see where the snow is, and in some years there is not enough anywhere to justify travel or lodging cost. If you want to ski the WROD anyway, do it somewhere close to home and cheap, because that's what you will be getting at most destination resorts that early. Thus if it gets much into December without much natural snow and I'm antsy to ski, I'll drive to Big Bear for a day rather than make the longer trip to Mammoth with lodging cost for the same kind of skiing.
If there is abundant snow in November, sure you can make a last minute call to get some of it. It's still a holiday though and will be busy. Skiing in November is icing on the cake and relatively rare for me. I often take non-ski vacations in November. If you have to commit $$$ in advance for Thanksgiving, do that for a less speculative activity than skiing.