OK so I'm not normally a dungeon maker but I thought about trying to stretch myself. And because I don't want to start doing buildings with all of the junk to fill it up I thought about going back to when I was 14 and loved doing dungeons on graph paper. I drew some random shapes in white on a black background, hit it with the crystallize filter a few times to get a rough cave lookin thing. Overlay a graph paper pattern and viola...old school dungeon.
I then started to apply my usual style and came up with the second thing...needs some work but it's my first attempt.
Nice start. It does add to the feel of the cave atmosphere. The thing I think that I notice though is that it seems a bit too sharp and artificial. That's probably the bevel though. An idea might be to do a height map instead of a bevel. All the solid rock areas would be max height while the cave paths would be low points which rapidly but smoothly moved towards the high points.
Here's an example of what I mean. Not exactly the fanciest since it was rushed but it gets the idea across (I hope anyhow).
It's too Dark! (C'mon you knew that was coming...:D)
Seriously though, I'm liking this, though I do agree with Nomadic about the bevel. Not sure if you need to replace it with a height map (always an option), maybe just reducing it will help some.
You could try experimenting with the bevel contour a bit.