If this is the second hardest club in the USA to get into, it's simply because Disney limits membership intentionally -- they could build another "exclusive" restaurant or two and easily increase the size. Another reason the wait is long clearly would be because Disney top execs use it to impress people or as a business entertainment venue.
It started for Friends of Walt, and was (probably still is) the only place inside Disneyland where alcohol is served.
And like everything else, for the proletariat, Disney sells it at a substantial profit. They know you aren't going to give away all the passes; they totally come out ahead.
So if you can afford it and are a Disney fanatic, or want to impress the few people who know about it, go ahead and join. Otherwise -- you can get some really nice vacations for that money.
P.S. I grew up in LA and was also Disneyland-addicted -- when I was under 15. I still have some remnants of early ticket books stored away somewhere. My father practiced medicine in downtown Burbank and Walt's brother (the original Roy) used to patronize the foot doctor down the hall.