Well, incorporeal beings don't have much to be seen, what you actually see is pretty much a projection of your ideas about that spirit anyway:
And you don't actually need to see them, just to locate them to use magic upon them. So you could downgrade things a bit, and instead of...
...use a R: Smell, D: Mom. version which would be 15 levels easier and should be enough to give you a scent you could use to target the spirit.
But the easiest part is to trace them by their powers, as One Shot says: it's the only way they can interact with the physical world and, hermetic magi being part of that physical world, that interaction can go both ways. But always also try the yet one more Arcane Connection to your collection approach. The more the merrier.