Good points Brew, Sean, Meta & atayl0r. I agree with all points... except even with big numbers at Boggs, after the first lap, things spread out fairly quickly and traffic isn't a big deal (in my experience). But that's an 8 hr race. Maybe Sea Otter is a better example of too many racers on course. While I don't think a race like Cool will ever draw 800+ racers (unless it was highly marketed to the high school teams/league), it perplexes me that there are lotteries to run 31-100 miles, and road centuries often pull in 1,000+ riders, and now Gran Frondos are exploding in popularity... yet MTB races often struggle to draw participants, like the Big Sandy Race seems to be currently facing.
I think you guys hit the nail on the head though... most mt. bikers love to ride, but not necessarily race as fast as possible in a competitive environment. In the running events, centuries and Frondos, "To finish is to win" is an important motto to understand. I think Northey made a good decision to turn the Tahoe-Sierra 100 (and TS 50/50) into a well-supported adventure ride (even though some racers will be pissed). It'll appeal to a larger audience of riders and hopefully draw a quite a few more people seeking the challenge and sense of accomplishment. Now we need to figure out how to help him market/promote it better!
Bike Monkey is doing a heck of a job marketing their events. It's very impressive Boggs sold out long ago. I do think the draw there is a combination of 1) good marketing; 2) pretty fun terrain/course/location for a loop race; 3) the party atmosphere; 4) not too far away from anywhere; 5) "it" factor... it's become a tradition of sorts for people and bike clubs who come out in droves (see #3)... similar to Sean's references to the popular MTB endurance events.
Note: I'm not complaining about race attendance... I think we all enjoy the small, grassroots feel to our local events. I just was curious what other people's take on the difference between MTB events/races and other not easy/not cheap events were. And I do have a soft spot in my heart for race promoters... a lot of them work their tails off with little appreciation and $ to show for it afterwards.