I think the whole unexplored wormholes on an unexplored planet thing is a bit of a sloppy way of doing things. Yeah, there's the unexplored nebula adjacent to the planet, but there are also potentially more unexplored wormholes if you haven't scouted over there yet. It doesn't make any sense, and I really don't think it should be set up like that.
I'd prefer it if, say, you could make nebula systems visible with some kind of effect (shadow vessel only, so maybe some darkness behind and a bit around the planet?) and put a separate filter in for nebula systems. I think that would be nicer than using a filter for something that's rather unintuitive for the filter's name.