I'd say the biggest driver here is simply that most Rush fans are in their 50's/60's and that's the stage of life where we tend to have the most disposable income. I know of a number people who are digging deep to go because it's that important to them, and it's tied to their youth. It's expensive for a concert ticket - too rich for me - but if you buy it as part of the annual couple's vacation or something it probably sets there more neatly.
FWIW, I always took the "tan pants" comment to mostly refer to poser guitar players who bought lots of cool stuff but didn't have much background, not just someone who makes a decent living. I'm not certain anyone can complain too much when they're out there buying the latest fancy metal amp, even if it doesn't fit in with the "boutique" crowd, or buying US Jacksons as opposed to PRS guitars.