I've worked the ASA booth there the last 3 years and will be working The Clean Dune Project booth there this year. It's a camping weekend for me (on the others side of the tracks and away from the dust), I do not even unload the car - the dunes are a complete zoo. If I had to guess, >90% of the current membership in here avoids that weekend like the plague.
As far as setting up shop and spreading the gospel or selling merch, that's a horse of a different color... they'll have a compound setup behind the beach store with a frickin ferris wheel, several vendors, giveaways, demo-rides, free service bays for Polaris vehicles, a stage for a concert, etc etc with numerous vendors set up inside... SandCraft, Rockford Fosgate, RideNow, Bert's, food&bevs, etc etc... based on the last three years the overwhelming majority of people that come into that compound are first-timers or pretty new, uninformed, but open to conversations and willing to get educated... the dunes are littered with fools but the ones that come inside and walk the compound are actually looking for deals and info about the area and the sport, I've been pleasantly surprised at that part. They'll give away everything from yeti coolers to a new Razr and must be present to win... so an audience is guaranteed.