I think that you may have a point about the bloom being off the rose for the more frequent visitor. I know that I am more likely to notice imperfections the more often I look at something. It's one of the reasons why I'm considering cancelling one of my two remaining trips this year.
However, I can say that each of my visits over the years has had its own uniqueness, whether it was the first time that we took the kids when they were all under 6 or a last-minute girls' week in early January with my sister because prices were so low. There has always been something new that I got to try each time.
I don't think it's entirely due to that. I also think that the outside travel world has caught up to what use to be Disney standards.
for example, look at the difference in the Deluxe resorts and the Waldorf Astoria right outside disney's gates. Now outside of location, Disney just is not up to deluxe standards so it gets hard to justify paying 500 bucks a night when you know what it would get elsewhere. Before my dh got ill we took a mini vacation to the world, since we wanted it to be a bit more romantic we stayed at the WA. 189 bucks a night!!! that's pretty much moderate prices. My dh said, no way would we ever stay deluxe on site if we weren't using our points.
Now like you said some times I do notice "little" things but some of the little things are what use to set Disney apart. Another example, we use to use valet parking all the time, now I know for most folks valet is an incidental but when you travel with a handicapped aunt with mobility issues, valet parking is not so much of a perk. anyhoo, when the servers were disney employees it seems to me they were efficient and polite. 7 mins top to get your car. When they outsourced them, it went waaaay down hill. Now they tell you to factor in 30 minutes to wait for your car!!

really 30 minutes, at the Grand floridian? supposedly your top of the line resort?
And I don't think you can really find anyone who would argue very hard that the food quality has not declined.
I think one of the issues those of us who are long time repeat customers have to grapple with is that Disney used to actually be the measuring stick family vacation places used. Not so much now.
Now we still have a great vacation when we go, but I would no longer call them "magical".