Most times when any attraction is "Closed for Refurb" it has little to do with "adding features" or "changing" the ride, and more to do with "making sure the tracks at the front of the ride are still firmly connected to the ones at the middle of the ride, so your vehicle will smoothly reach the end of the ride."
Space Mountain at WDW has been "refurbed" many times in the past few years, but the kind of CHANGES made at
Disneyland have not been implimented.
Painting, new seat covers, a good cleaning of the ride and the queues are usually included.
There are exceptions:
Small World (at WDW) just had a major "make-over" last year.
Pirates (all Parks) MAY or MAY NOT have some Johhny Depp-from-the-movie additions (this has been seriously rumored for a long time.)
Enchanted Tiki Room, Under New management, was a big change.
Living Seas at Epcot is being "re-engineered" with Nemo theming.
But many times, the "refurb" is just a "make-up and foundation job"... not a whole NEW MODEL.
