I think when you talk about this issue, you really can't speak in terms like "it isn't as good as it used to be" or generalizations like that. It is more complicated than that. That being said, I don't think every change that has been made at WDW is for the better. I perfer Horizions to Mission Space, I perfer World of Motion to Test Track, and I perfer Mr. Toad's Wild Ride to The Many Adventures of Winnie the Pooh. By no means do I think Mission Space, Test Track, and Winnie the Pooh are "bad" attractions. Actually I like all those attractions, but just not as much as the previous ones they replaced. Is that nostalgia? Maybe, but I just like those old ones better. That is just my opinion, most other people may like the new rides better and that is ok. I am not whining or complaining that those rides should never have been removed, I accept that they are gone and it won't prevent me from enjoying WDW.
What I don't understand is the mindset that "everything at WDW is great", "every new attraction is great" and "everyone who expresses an affection for an old attraction is wrong and stuck in the past". I feel it is more complicated than that.