We've enjoyed DC many times during the time period you reference. other than the photos pkg costing more and the design layout changing, can't say i've noticed any dip in quality as to food or service, nor did it seem more crowded overall.
will say the snorkeling area can get congested, you need to time it. If it's busy, we go do something else and return later.
it could be since we don't have long stretches between visiting, changes aren't as visible to us. I honestly notice a lot more changes between several disney trips each year, some good - some bad lol.
DC is very expensive, we've never felt tempted to add on cabana rental, etc. and we feel the day is enjoyable as is.

IMO DC provides an amazing experience overall.