I think Western River Expedition would work perfectly for the expansion pad between Grizzly Gulch and Adventureland. Together with Mystic Manor, this addition would significantly enhance the perception of HKDL among Disneyphiles.
I'm sure frequent visitors to the park like SirEdge or Timmy could back me up on this, the wait times are solid (peak days 40 mins, and 40 mins is considered ALOT at HKDL). Around evening the crowds thin down at the rides and head over to Main St. for the fireworks so the wait times are considerably lower after 6:30ish.
Yup! Longest I've had to wait for Space Mountain is 20 minutes. The longest one I've had to endure was 45 minutes for Toy Soldiers Parachute Drop, when it first opened. Compare that a couple of months after IJA opened, the queue was 2+ hours. I know IJA and TSPD are like comparing apples and oranges in terms of ride quality, but it should give you an idea what kinds of rides are popular in HKDL. I didn't even dare try to line up for Slinky Dog "Coaster."