Astral projection is one of those, for me. I see it, and it is itself, a much of a muchness, and what else is there to say?
Don't know. So let's look at it. Here's the power description for Astral Projection, from ICONS: The Assembled Edition.
Astral Projection can send your astral form (the vessel of the mind and spirit) out from your physical body, allowing it to travel elsewhere. Your astral form has Flight and Phasing at your power level and full Life Support. It can observe, but not affect, the physical world and cannot be detected by physical means, although Spirit Detection and Telepathy reveal it and you may choose to be seen and heard, when you wish. You can use mental powers against non-astral beings, but with +2 difficulty. Your powers work normally against other astral beings. Your body remains in a coma-like state, although you are aware of any harm befalling it. Should your body perish while your astral form is away, you remain trapped in astral form.
First thought: I didn't realize it, but Astral Projection is pretty good for a ghost, actually. (Kinda like it's made for them.) Flight and Full Life Support and Phasing? In a ghost, the fact that your body has perished away is taken for granted. Next time I have to actually design a ghost for ICONS, I'm heading for Astral Projection. I can still think of situations where it wouldn't work, but they're rare. (And add a possession power and you have Deadman.)
Second thought: It and ESP have a fair bit in common. If you have, say, Astral Projection and Mental Blast, you might well get a closely similar effect from ESP, Mental Blast, and Rangeless. The ESP version is easier but Astral Projection has more range, though: you are limited in how far your ESP goes, but not your Astral Projection. (It's a plot device if either ESP or Astral Projection goes to other worlds.)
So you could use Astral Projection as a gadget that places your "awareness" (not in the game sense) in a different place. That would be a non-mystical way of doing it.
You could also have a Dimensional Travel that teleports you to the Astral Plane. Anyone with Astral Projection can get there using the power, but the Dimensional Travel ability moves your body into the Astral Plane. (Presumably there's some doubletalk explanation why astral selves sent out via Astral Projection work with the real world, while the Astral Plane starts out looking like our world but gets weird as you need it to.)
In fact, maybe the Astral Plane and the Dream Realm are closely connected: dreams sometimes leak over into the Astral Plane and vice versa. Something like that would make Astral Projection a little more dangerous: the astral self is in danger of being attacked by a rogue nightmare.
Like decking, travels on the Astral Plane read great, but they can be a solo event that the others only take part in. Be wary of that.