When my fork was being rebuilt, I showed up to a small local Enduro and XC race on "The bike of shame", which is a old, crap Raleigh I was given for free. Stripped down to single speed, 30 pounds, cantilever brakes, warped rear wheel running 1.95 Wal-Mart tires, and of course, full rigid. I "raced" the enduro Saturday and wasn't the slowest person. I raced the XC Sunday and was still faster on some climbs and decdbts then other people on multi thousand dollar bikes (I was the only SS, so if course I get first).
Do I have more fun on my Jamis? Yes I do. But people over exaggerate the importance of the bike.
My first MTB race was a 12 hour endurance (dropped out after about 9 with a broken chain) on a $450 40, pound 26" hard tail.
What I can say though is I would far sooner settle for a lower end frame and take a weight penalty and have high spec components (brakes especially) then a high end frame with low spec parts. That was something I learned after borrowing a friends Cannondale Trigger with low spec components compared to my "low spec" Jamis aluminum bike with X0 all around.