We were there last week - rope drop on a high-crowd Saturday, back of the pack because of transportation issues, on an 8:00 am opening. Space Mountain was a walk-on - posted wait was 15 minutes, but we walked right through the long waiting cue, and didn't stop until they asked how many in our party. Part of our group got off, and went right back on - 2 rides on Space Mountain in 20 minutes, and if they wanted a 3rd ride - it would have been the same thing - walk right through.
Part of our group went to breakfast instead of rides at rope drop - they still only had a very short wait when they went to Space Mountain after 8:30.