When it comes to feeling of speed, I also suspect it is the fake stardust but unfortunately, one can probably only do so much there. The original games were slow... but since everything was low-res and also running very choppy back then, things felt different.
Actually if it does turn out to be the stardust there's a lot we can do there; shrinking it and making a smaller volume makes it feel faster.
When the streaking engages that increases the sense of speed, but we only turn that on close to max speed, we could bring it in at lower speeds.
And there is nothing stopping us from cheating and moving the dust at double speed (right now there's no multiplier but it's an option). Like so much in the demo it's in the first passable state and hasn't been tweaked yet.