In my opinion, the Mansion should go down for a good refurb. Update the sound system a la WDW, new scene for the load area, install Hatbox Ghost, and get all effects in proper working order.
With this, The Mansion should stay its normal self until November 1 when it closes to install the HMH overlay for Christmas.
A Halloween overlay, in my opinion, is unnecessary because the Mansion should shine as it's decrepit, mysterious self during that season.
I agree, I think they should wait until November to install the holiday overlay. Keep the Hanuted Mansion the way it is now, it already fits the Halloween Time theme. But I do like imaginashton's idea.