I don't know how you have realized the heli's rotor but maybe if it is going to rotate faster you replace the model with the rotating blades (if the rotation isnt an animation in the model but a model of its own attached to the heli and rotated by script) by a discus-like model (over even a sprite?) which shows some blurred blades (done by texture) and an outlined circle rotating slowly and thus simulating the motion blur...

If you don't really understand what I mean here a picture which pretty much shows what I mean:

Here you can see the blurred blades and that kind of "circle outline" the blades do...

I think this would add a little bit of "communication" as the blurred blades tell the player that he now is going with high to nearly max speed and on the other side well "calms" the whole scene a little bit as u dont have this spinning all the time...

Antoher thing you probably have figured out too:
In your video at 1:38 the enemies' blades "refuse" to fall down too (as do the player's at the very end of the video)...