Please don't present your own speculation as fact. That's how really bad rumors get started. Considering every resort has gotten it's a small world holiday but Walt Disney World, and considering how insanely it boosts the attendance, I would not discount it as a possiblity. Obviously not for 2006 (and there-in lies the actual error) as it's already 12/7 and the overlay takes at least two weeks to install (and typically longer for a first time install).
Basing this solely on the "hasn't been updated since 1971" logic doesn't prove much- because by that logic Haunted Mansion, Snow White, Peter Pan, etc, etc all should have closed for the sound system upgrade. Plain and simple fact is that if an overlay *were* planned for the future, such a referbishment would be the required first step.