Yeah, there are a lot of DL Mansion purists that don't like the concept of the HMH overlay either. I would NEVER want the overlay to be permanent, but it's a nice change for the holidays and something I look forward to. I completely disagree that it's a "tacky" overlay, but obviously that's my opinion. The outside, I might give you some points there in that it kinda does have a cluttered / chaos look, but given that "when Halloween creates Christmas, you might see a few flaws", I think that was the point. Walt would have freaked, though, haha, given original plans for our Mansion's exterior!
But the interior is hardly something they just throw together. It is very thorough, very meticulous, and not cheap. That said, they have done this enough now that it's gotten more and more efficient. This year, Mansion went down today (Sept 4), and will re-open Sept 21. That length of downtime would hardly be an issue for Florida given that this marks an off-season period for Florida too. The reason that I was given before is that, in their words, Florida doesn't need to. Locals are not as big a segment of overall revenue and therefore the need to constantly provide reasons for guests to come out is not as much of an influencing factor. One might argue a translation of that stmt is that it's OK for WDW not to keep things fresh, that it's OK not to "plus" things, that it's OK to stagnate for a little while.
That's why Disneyland does so many special "little" things, because it brings back locals; whereas WDW visitors are not going to plan vacations around "little" things. That said, HMH and SWH certainly started out being "little" things but are now MAJOR holiday attendance drivers. Combine that with our other "little" things like the Reindeer Roundup, Believe fireworks and snow, and Christmas decorations literally in every land, and you end with November and December becoming a huge 2 months worth of attendance vs just Thanksgiving week and the 2 weeks of Christmas as in years past. Disneyland regularly reaches capacity on Saturdays during these 2 months, and during the major weeks of the season.