TS&M - a lot of what you say is good and true.
All you have to do to keep your cave cert active is do 8 or 9 cave dives a year, or 25 in a long, single trip every THREE years. If you do this, there is no need to retake a class.
But if you don't, it will probably be expensive to get your ratings back.
I think it's a GREAT idea to provide a motivation for people to stay current. If you took a cave class and then didn't cave dive for ten years, would you think you could go right back to it? Having a day or two of checkout from an instructor would seem to me to be a very good idea.
My motivation in cave diving is to enjoy the caves, the skills challenge and to be safe (and stay alive). When I feel rusty, I will go to a pool, find a mentor, and do fairly conservative dives until I am once again confident. I even retook a course (different instructor - different agency) after a 7 year absence from diving. My original cert (NSS-CDS) was still valid. As a cave divers, we learn and are trained to be aware and self-reliant. I do not feel I need an agency (GUE) to tell me what I need to do and when to do it.
Good and safe cave (and other) divers do not pop out of classes, no matter how good the instruction. They need to incorporate and integrate what they have learned and evolve through experience. It is also said that it may be a good idea to not have the same instructor in subsequent classes as to learn and experience different viewpoints and approaches. While the training GUE provides may be superb (I still believe that the instructor is the key factor), I am not inclined to follow a single path (or agency) and have them make decisions for me. I have been diving for 40 years and have seen a lot of changes to believe in any one system.
Yes, this makes a tiny bit of money for GUE -- maybe -- because you pay a fee for the new card. But that's not why the requirement is there. It's part of the overall attitude of the agency, to make sure the divers they train are on top of their game.
While this is a noble sentiment, I am cynical enough to not believe it. Any agency's primary function (whether stated or not) is self-preservation and perpetuation, regardless if it is a church, political party, government, etc. Many of the diving agencies have policies that are basically CYA - that is, to limit their liability and I believe, to generate revenue. GUE 3-year expiration, NACD and NSS-CDS temporary doubles and apprentice levels are examples of these. TDI has cavern, Intro-to-Cave, Full Cave (no apprentice or configuration exclusions). NAUI and IANTD have Cave1, Cave2, etc. It seems that the path to full cave certification has been obfuscated by lawyers and the desire to feed the training cash cow.
If the OP desires GUE training, he should pursue it. I would actually love to take a GUE class if the cost was not so high and they did not require back-mounted doubles instead of sidemount (another silly artifact of institutional cement). I just caution against taking ANY organization too seriously.