You will enjoy it! My first trip to the Nationals was at Park City ten years ago. The only year I've missed since was 2007 when some broken ribs necessitated canceling the trip. I always "double my pleasure" by entering both as a skier and as a boarder.
The organizers have fine-tuned the whole event so that you maximize your enjoyment of the experience. As others have mentioned, you'll be racing Blue Grouse which is the normal daily NASTAR course. It's comparable to typical venues around the country. Give it your best shot but don't get too focused on your results. If you make the podium consider it a bonus.
You'll get the chance to rub elbows with the likes of Ted Ligety, AJ Kitt among others. You'll find them genuinely nice folks and more than accommodating when it comes to signing autographs.
My guess is that this won't be your last trip to Nationals.
When you get out there look for an elderly snowboarder in a bright lime green jacket!