I call things excuses when it fits. Since you just admitted you've never helped set up or run a competition, you don't have a clue as to any of the logistics or anything else.
I, on the other hand, have been involved in setting up national boating competitions and state square dance festivals that are still larger than your so called nationals.
90 db is an issue? My boats have to be at less than 90 dbs as well or they will be disqualified from competition. When you consider that I run all CMB .67s in my boats with 50% nitro fuel at up to 28,000 rpm, you would think that would be an issue, but it's not. If the planes can't get down to 90, it's time to change something, either the muffler/pipe or the prop.
Obviously, you didn't look at Fort Casey. There's plenty of room for everything needed to fly gliders in competition.