We did the same thing as a team in 2017; mostly because our car wasn't ready in time. We only went for Sunday, which was nice because we got to see all the cars come in and cheer them on, but also a little awkward because the majority of the teams were exhausted. Nobody was mean or anything, but I think you'll get a lot more of the energy and excitement coming down for day one.
Before coming down, bring a lot to drink - you will get thirsty walking around and talking to people. Also bring ear protection, comfy shoes and just as comfy warm clothing. Forecast calls for icky so take that into account as well.
If you already know what kind of car/team you want to race with, research the teams that run the same or similar. We picked up a VW Fox and then got in contact Tom Lomino of Farfrumwinnin who used to race one before wisely switching to the Jetta. We also chatted up a team running a Sirocco and between them and a bunch of other helpful people got a good idea of what to anticipate breaking during a race (that is, if you actually run for more than 30 minutes at a time).
Don't only talk to teams about their cars, but also their themes. Take pictures and post them to the Facebook event and forum. Take notes and names.
As everyone else said, check out the Saturday potluck and awards ceremony. To my knowledge, there's not much of an afterparty unfortunately, because everyone wants to get back home and work the next day. Also no alcohol consumption in the paddock while the track is hot, which is kind of a bummer but totally necessary.
Come check us out, FMC racing, we're splitting Garage 8 with Squidrope racing. We'll have food and bad jokes. We actually had a spectator buddy up with us at Thompson who was super cool and he'll probably be there this year too, so I think you might have the makings of your own raceteam in the works.
March 2016 bought running 1988 VW Fox Wagon
March 2016 - Spring 2018 Car was on its side with no engine
2018 Thompson Organizers' Choice (25 laps)
2019 Thompson Judges' Choice (58 laps) NHMS Judges' Choice (74 laps)