Sorry, random passer by who is quite interested in this game...
Wavefronts.
They can still exist within your "they make the player slower if they mess up" idea.
Make them somewhat rare, and more of a navigational hazard. Keep the idea of they can speed you up, but, just like real waves, they are only useful if you don't have a destination (other than not here).
Useful for people who just want to get away from here as fast as possible, or people doing somewhat random scouting. For people with an agenda, who just want to get from A to B, or people on a time frame, they are a nuisance.
Also really useful for people wanting to make a looong trip. No good for starhoppers.