Yes. Minders, except for the Pros, are in my experience, generally discouraged. There have been many issues with too many minders in sections and on the loop. Lower class riders shouldn't need minders. Lower class riders should develop their skills locally and practice on obstacles that will be harder than those they expect to ride at a Nat'l. They shouldn't need a minder to feel safe while riding a Nat'l.
Entry fees for Nat'ls have been significantly reduced in recent years. Given the attendance level at this year's Nat'ls, I expect that the host clubs are barely breaking even. If they weren't closely watching their expenses, it would be possible to lose money.
Stadium style events - been there. Minded for a rider at the 2nd event at the Cow Palace in SF. I enjoyed the experience. However, my understanding is that all of these stadium events in the US have been significant money losers. Those who have promoted these events, most likely with the expectation that they are taking significance risks with their money, have my admiration. However, I do not recommend hosting one here in the USA unless you are simply willing to toss $$$ away in the effort to promote the sport.
Trials has to be one of the most inexpensive motorsports on the planet, if not the most inexpensive. Tires are cheap. The vehicle is cheap and competitive in stock form. At the peak of my trials riding experience, I went through 4 sets of trials tires in a season - maybe, $800 - $1,000. I can spend that on one set of tires for autocross; if I was competing Nationally in Autocross, I'd need a fresh set for every weekend... National level karting would eat up that much $ or more in tires in a weekend or two at most and the rebuild frequency would shock you.
Spectating at a Nat'l Trials is also cheap. I spent $60 just to park at the MotoGP in Austin this past April and that doesn't even include the pair of grandstand seats for 3 days... I think the total for my wife and I was about $400 for the weekend.
Please remember that trials riders can't always continually improve. As one starts riding, with significant practice most can see improvement. However, that improvement can not be sustained over many years. As one gets older, perception of risk may change as well. Please consider that it's important to find places for those riders that are moving down to ride less challenging lines, else they have to disappear from the sport. Personally, I'd rather have "Sandbaggers" showing the newbies how it's supposed to be done as opposed to running off those that have invested years of passion in the sport.
Sorry to be so negative, but I've heard the same complaints over and over and I've only been riding trials for about 20 years. These complaints are often from riders that are just getting started in the sport. Trials events require volunteers. Be involved. Volunteer. Promote events. See how easy or hard it is to make a difference.