The only facts I know is that the Haunted Mansion is rough around the edges and that it will be closed for a little over 3 months, which should be ample time to have it looking and working the way it should, both visually and audibly, if not better. Any additions or extras are special bonuses imo. The "major" changes at Disneyland's HM over the past 2-3 years I wouldn't even consider that major. They were simple enough to be installed either during the night while the attraction was still running during the day or when it was down for its relatively short NBC overlay removal. I would be incredibly suprised if during this 3 month time that they couldn't find the time, or the money, to install a floating Leota head. Of the DL changes in which there is a comparable scene at the MK, that was the only one that I was really impressed with. The attic changes were neat, but nothing spectacular. I was actually a bit disappointed with the new bride in person and prefer the floating, nonspeaking, heart beating bride in the MK HM. For me, it was an example of where "new" technology did not necessarily create a better scene, even though the changing portraits in their attic are really neat.
A new graveyard scene, a new queue, a new exit with a grand gift shop, a new scene for the spiders were all internet rumors imo with nothing to indicate that they were anything beyond blue sky rumors, if not just fan-spawned rumors. NONE of that is anything I would expect from a 3 month rehab. At the most, I expect a HM that looks and sounds like new, with updated audio, rehabbed sets and animatronics, and possibly some of the minor changes that DL has received, most notably the floating Leota head. If after 3 months there isn't a noticeable improvement in the attraction's quality, then I think there is a reason to be disappointed.