The movie doesn't matter, the ride "was" Disneyland.
I have never seen Song of the South, but this song brings back all my Disneyland memories.
Splash Mountain was made with re-used animatronics to save budget. This gave it a somewhat modern "retro-mod" vibe. 30 years after opening, it's pretty much "classic Disneyland" now and there was no reason to update it. It would be popular for another 30 years, old animatronics and all.