I am against Holiday overlays in general, with the exception of perhaps Small World.
Why? because they destroy the original ride's architecture and concept, and they look cheap (because they are temporary and *overlaid*). This is not such huge problem if you are an AP since you can just come back later in the year to see the real deal.
But it is really unfair for all our guests that only get to come every Christmas, such as many Australians and Kiwis (whose summer is in our winter). Imagine only ever seeing HMH and thinking that was it. A ride with a bunch of plywood cutouts and fake snow thrown around. And never knowing how truly awesome and realistic the real Haunted Mansion is.
Even if you like HMH, you can't possibly say it matches the original imagineering wowness of the Haunted Mansion. But if you were from Australia, that might be all you ever knew.
Anyhow, Adventureland should look like exotic places in the world... like equatorial jungles, etc. Once you start putting Christmasy elements in there, you'll ruin that. It doesn't snow in the jungle of the Jungle Cruise (wrong part of the world). Really subtle and realistic touches (such as the radio broadcast) would be lost on guests, and thus pointless budget-wise, but they wouldn't hurt.
In the end you must ask about Integrity. Does the overlay destroy the integrity of the original attraction's theme, tone, quality, or concept? I believe that in the vast majority of cases, the answer is absolutely yes.