As other's have pointed out, DCL has to walk a fine line to keep all their interested parties happy (customers, employees, stock holders). Personally, I think they have
Castaway Club because it is the norm for cruise lines to have a rewards program for frequent cruisers. If DCL could get away with not offering it, I'd think that they would. But as they chose to play the game, they need to play by the rules set by the industry.
On a whole, the club doesn't seem to be well managed. Yes they have gifts for silver members, early book for gold/plat, and plat get a Palo meal with a private-ish line at the terminal. But they advertise that they'll send out an e-newsletter, but it hasn't been updated since the Summer of 2014. They advertise that CC members get their own phone line, but once you enter your CC number it routes you to the normal line. Even the fun download sections have very little to actually download.
Frequent buyer/flyer/cruiser programs are designed to retain current customers. Typically, it is far cheaper and more cost effective to keep current customer's happy than it is to attract new customers. However, Disney is an exception to this rule as there will always be new customers to replace those that choose to sail with other cruise lines. Disney knows this, as does many people who frequent DCL cruises. My friends who talked me into doing a DCL cruise as our first cruise said they keep cruising with DCL because they love the ships, the atmosphere, and a who laundry list of reasons. But they did not say they sail because they love the CC member benefits.
As for the inequality argument. This is a fact of life in a capitalist society, some have more than others. And if you can spent it, why not spend it? I'm not rich by any definitions so I doubt I'll be sailing concierge any time soon. DCL has the concierge class cabins to allow those that prefer to spend more to get more to do so. Every industry has this, so when I hear about people yelling at cast members because they can't visit the concierge lounge, it upsets me (I witnessed this on our cruise as well. I had to fight back the urge to jump to the defense of the CM).
I'll get off my soap box now.