Sean,
I think you make a few whopping assumptions in your post, which can be interpreted as another version of the old dead guys were just better.
I would like to go to Wexlers book today and see how many bunkers AM's last public course designs had. Or look to see how many, other than the black course, Tillie put at Bethpage, since the Black was part of a multi course complex and specifically intended to replicate a public version of Pine Valley, etc. For that matter, how many bunkers did ANGC have in AM's last private design? Didn't Ross and those guys write about not piling up a score? How many bunkers were on the typical DR course?
If the number of bunkers is less today, it may be for budget reasons. If greens are flatter, its probably due to green speed (and even BP Black's were a little flatter than Tillies other greens)
It isn't all black and white in making a design more accessible for more players. Its using features that still trouble the good player while not killing the average player. IMHO, that includes reduced forced carries, open front greens, gentle, but not flat green contours, a few less bunkers front right of greens (but possibly replaced with chocolate drop mounds, grass bunkers, etc.) Wide fw are nice for a lot of reasons for all players.
The design features used for a good, but not tournament test for good players are not that much different than those that allow average players to play. Frankly, I think the average Brauer (and others) public design has plenty of design interest and are far better than their 1920-1970 counterparts (in general, as there are always exceptions.)
And the point about a designer designing for his intended client and future clientele isn't a cop out....its valid. I think one of the knocks on the CCFD was that they were often designed for a tournament that would never come and were too tough for even good ams to enjoy, wasn't it? Making courses the "right" difficulty for the golf world is a noble endeavor. Is it noble to design a tough course for a tournament that never comes, or for 1500 gca.com particpants who think every course ought to include a bunch of old time features? BTW, I do think gradually introducing golfers to some great features is a good idea and have done it.
Short version - "Dumbed Down" or "appropriate difficulty for the fun and enjoyment of the masses" are both pretty subjective terms, as is "good design."
Sorry if I sound like I am ranting. Not a bad subject, but I will put, say my Sand Creek Station, and its design concepts, aesthetics and general quality against a lot of courses. None of their players seems to think they have been shortchanged in that department. The same can be said for many other public courses.
I really don't think any public course by any recognized designer in the last two decades has been dumbed down to a large degree, because quality was the main selling point in most of those business models. That may change in the near future, as I get a lot of calls for bunker reductions, removals, etc. now.