If we're going by textbook definitions, I don't think any Disney resorts have ever met the five star criteria.
Nevertheless, I do understand what you're saying about reductions in quality. However in fairness I think those losses need to be balanced by gains made elsewhere. Just off the top of my head, we've received upgrades in things like sofabeds, most resort mattresses, iHome radios in the villas, sleeper chairs, extra bathrooms in newer resorts, better patio furniture, better cookware, appliances, flat panel TVs, and so on.
Heck, even the addition of new resorts is a major plus for the program. Sure the cynic would respond that the only reason we have more resorts is because those greedy suits at Disney want to make more money. But those who bought into OKW nearly 20 years ago did so with the knowledge that it may be the ONLY resort that would ever be available. Now they have 9 more native destinations with more on the way.
I would count myself among those who are mystified by most others' experiences. Our vacations have not all been flawless, but Disney has handled every issue encountered with the appropriate level of attention and care.
Perhaps the most frustrating aspect of these threads is that (in my opinion) it gives a distorted impression of the service offered by Disney resorts. There are something like 4000 DVC guest rooms in the entire program at this point. That means tens-of-thousands of members + family staying at a DVC resort every week.
Disney isn't going to have a perfect track record with regard to maintenance and housekeeping no matter how hard they try. I don't mean to trivialize the experiences of those who received a dirty room or broken appliance, but those instances are still
far in the minority.
When members run into problems they should absolutely send emails or letters and speak to management about the problems. No argument there.
But the best thing folks can do to protect themselves is gain a better understanding of how to get problems resolved and, even better, prevent problems from occurring in the first place.
One of our family doctors has a sign in the lobby which reads "your lack of planning does not constitute our emergency." Not exactly the most customer-friendly slogan, nor is it anything I would expect to hear from Disney.

But it's a pretty good philosophy to keep in mind.
If you know you often need extra pillows, check them when you arrive and call immediately--don't place a call 5 minutes before bed and expect them to arrive in seconds. Check for important amenities like hairdryers, cooking utensils, towels and dishwasher soap well BEFORE they are needed. 99% of the time housekeeping and maintenance will have done their jobs and all of these items will be present. But a little advance planning helps guarantee that you aren't left with a pancake you can't flip because someone swiped the spatula.
Although it's been said a million times, anytime you have a problem that isn't resolved promptly on the first attempt,
PLEASE go to the resort front desk and speak with a manager personally. I cringe every time I read stories from folks who called maintenance over and over again without getting the problem resolved. Just get a manager involved.

Come to an agreement over the timeframe in which the problem will be addressed. If the don't perform, camp out at the front desk until they DO perform. (I've never had to make repeat follow-up visits to the front desk but it just mystifies me as to how people allow problems to continue for days on end instead of insisting on a proper resolution.)