Comparison between Insubstantiality and Astral Projection

[phiwum]

How about this?

If you want to know what's on the other side of a locked vault door, Insubstantiality will do the trick quite nicely. Most of those who've given an opinion don't reckon that Astral Projection is useful for this task.

I think there are a number of times where the cost of Insubstantiality is worth it. But probably few of those are in the throes of combat.