If I were in charge, which I'm not, this would be my plan for fixing SM.
1. The queue must be reworked to be state of the art. Those 1980's illusions just don't cut it anymore. Really make this queue area very engaging and feel like we're really entering a space station loading platform.
2. The track doesn't need to be gutted as I like the layout of SM, but it either needs to be fixed or replaced so that the ride is ultra smooth.
3. The lift hill either needs to become some type of launch hill (which can't be done without changing the entire track) or better yet, use the technology from Everests climb hill to make it very quiet and then use the speed room technology to make it look like we're climbing very fast.
4. Place some nice theming throughout the ride so that its more than just darkness and on ride audio would be a must.
5. Replace the trains and the entry to look much cooler. I absolutely love Tokyo's new trains. I'd say use those.
6. The Post show when it was the RYCA1 Family of tomorrow used to be an attraction in and of itself. In fact people were encouraged to go through the ride even if they weren't going to ride it just to see the post show. The cheesy duct-taped tvs we have now just doesn't cut it. Make a very nice, sci-fi space station or something similar to be a great post show worthy of being an attraction in and of itself again.
That would be my refurb.