Space Mountain has been open for 36 years and it's still one of the most popular attractions in the entire resort. I think the only rides that routinely match it for wait times are RSR, Indy, and TSMM. Space is the only one of those rides not based on a film and the only one without recognizable characters. And yet, it routinely has 60/90/120 minute waits, even at the end of the night.
It's just that good.
This isn't about nostalgia and it's not about aversion to film/character theming. It's about recognizing that the ride is excellent as it is, it is clearly NOT struggling to draw guests, it stands up to the test of time and the public's tastes, and it should be left as is. If they want to renovate or add an overlay I'd expect and hope that it would be original to Space Mountain, the way Ghost Galaxy is, instead of being themed to a disparate film franchise.
If they want to add another SW attraction or coaster, they can build it. They don't need to shoehorn it into an existing, thriving attraction.