Friday is something that you really have to be careful with, just because of when the regionals are scheduled. Fridays for Catholics are no-meat days. This problem came up in Wisconsin when within a half hour they ran out of all non-meat dinner options (and had to order more). As long as you take this into account, a Friday should work well.
A different location is fun because it’s a change of scenery. The problem is, especially if you have a lot of teams from out of the area, you need very good directions. Also, if it is a choice between charging extra for an off-location social, or a free on location, you have to go with free. Few will pay for the extra.
Why wait until the pits close? Typically, pits close at 8 pm (in my experience). There are few who are left in the pits near the end, starting before the pits close wouldn’t be a heartbreak. Just make sure that those who need to be in the pits until the end still have access to the food!
Free is pretty much the only way a social will work. Your social is fighting with a scouting session or a free swim in the pool back at the hotel. The committee needs to make every effort to make the event free.
Anything that you’ve got is great. Wisconsin did a pretty good job with letting us check out the exibits (mating monkeys go over well, btw) and had DSKB. Something like a dance, games, all of that would be fun. Play-station/Xbox tournaments, DDR, make sure that you get things that multiple people can participate in at once.

