Blkdraco,
Wednesday night is usually the least important of the nights. So, if Blackdove were to miss one, that would be the night to miss. Honestly, there's rarely much going on.
Saturday, however, is a big deal. Usually has the Hugo awards. So, if I were you, I'd not want to miss it. If you're willing to foot the bill for the car, then that's great. Though, I still think that some of the others of us should chip in--particularly those who aren't themselves driving.
So, the rental seems the best choice. You ride down with Old One, then drive back up in the rental. (Though, there is usually a rides board and the like up at one of these things, and so I can look and see if there are any other Utah people I know who have driven down.)
Though, as I think about it, Blackdove could always catch a ride down with Old one, then back with his family (if they stick around Saturday night.) One reason I mention this is that sometimes these things sell out, and so he will want to be there Wednesday if possible so that he can be sure to get a ticket.