I've never done a mountain bike event that I thought was anything but fun before/after. I believe the atmosphere is mostly contained in the people that attend the event. By and large, we have a good group of people at the events, so by default, the events have a good atmosphere.
I find this to also be true about the cross races. I don't think there's a bad venue out there in this regard.
i don't know smack about cross races, but IMHO there are two types of races - ones that are "fun" and one's that are actually fun.
sure you always have a good time on your bike, your racing, pushing it, blah blah, but there are events where i have walked away from and i am thinking about it for weeks after - i have had so much fun i'm not even focusing on what i am going to do for my next rides, because it was an actual really good time.
i don't x/c race anymore because of a few factors, but one of them is that most of the time, i just think its on the "eh fun" level versus something more like "having a blast".
sometimes the vibe is right at an event and there's cool stuff going on both on and off the trails, and other times the vibe is good, but just not all that super-special.
i agree, its the people at the event that make it, but i think the people throwing/running the race definitely have an effect on what happens with the vibe. the mtn man has a vibe to it, and that vibe starts with the planning/promotion of the event (heck its on the year-old website they have) and ends when they break down the last piece of gear. i think a promoter needs to put thought into that part of it. when promoters take that part for granted; that they will just let the event take on its own coolness-factor, well, you might as well put up a clock, have people ride around in circles for a while, and they'll all go home when they are done.