There seems to be a few problems with nationals that everyone is trying to solve here in different ways. Since I'm just a slalom skier I'm going to comment with only slalom in mind. With that said, here are the two main issues as I see:
1. The expense (both time and money) of participating in nationals for only one round of skiing.
2. The prestige and/or excitement of participating in nationals.
For the first issue, I would recommend some small changes. I was thinking that instead of the host site running a "practice lake", instead eliminate the traditional practice and change to a "qualifier lake". On that lake, run a qualifying class C tournament for every slalom division. Those qualifying scores would then be used to seed the nationals main event. I would suggest that the qualifier be a voluntary round and cost something similar to the practice ride. I think this would solve a few issues. First, I've never really liked how practices are run at nationals. Although SMRR did a great job, it always seems like a pain to buy a ticket, put your name on the list, and wait around for a couple hours for your turn to practice. So, I assert that this "qualifying" tournament could basically serve as your practice. If it was run this way, you could have your qualifier be the day before the "main event" and you would know roughly were you would ski. If you don't ski the qualifier, you'll be out early in your event. If you want to pay a little extra money, you'll basically get two tournament scores while you're at nationals. Also, the "main event" wouldn't really change much from how it's run today, other than how the order is decided. Additional practice could still be held on the other lakes after the regular "main events" finish.
The second issue is a much harder problem to solve. I completely agree that skiing at nationals with nobody on the shore isn't very exciting. I've had it happen to me a number of times for various reasons and it always feel like you're skiing in a regular "any weekend" class C tournament. In order to solve this, I think some larger changes will be needed. First, there probably needs to be some changes to the age group divisions so that divisions that only have a handful of skiers are merged with other divisions. That would result in larger divisions with more competition. Second, I would raise the level 8 requirement so that it's actually harder to qualify through the ranking list. I know this would reduce the number of people that could potentially go to nationals, but I think it might bring some prestige back to qualifying for nationals and thus motivate people to go who qualify. Next, I'd consider eliminating the MM and OM divisions for a national championship. The nationals has always been an amateur event and I believe it should say that way. For Open skiers I think we should bring back the US Open such that the world's best can ski there and for MM, they have the Big Dawg. Perhaps bringing some of the OM and MM back into their age division would bring back some prestige for winning the national title in your age group. Finally, we've got to find a way to make it more fun to hang out onsite. Live bands, bounce houses, more food booths, games to play, holding nats at places with better weather are a few of my ideas. I really enjoyed hanging out on the bridge at SMRR and watching the skiers, but there wasn't a lot to do. Maybe listening to a live band would have kept me there for longer.