I think restrictions on how the rewind juice is used could make it more interesting to design around. For example have it be a limited resource and put rewind juice in places around the level. Or make it so in some areas it cannot be used.
I don't think a red outline would be good specially since you enjoy surprising the player and telling them ahead of time of the danger would defeat the purpose. The thing right now is that dying is inconsequential. I believe that putting some way to make dying sting just a bit more would make all those enemies and dangers click better.