I was bored on a business trip, so I made some tiles..
http://home.comcast.net/~doho123/games/spelunker/newtiles.pdf
Here's a few notes:
All cave areas are pink. Intersections are purple.
The "full tile set" I decided is unneeded, since we are only dealing with paths and caves. Having tile edges that are just rock limits their usefulness, and adds many tiles that are not useful at any given part of the game.
I have grouped them in three groups. Group 1 are tiles that increase the flow of the game. These are commonly done by have cave areas that always have a path leading to them, so as caves are completed, they become intersections to other paths.
Group 2 are tiles I would regard as being somewhat useful, but they do not lead to combining pathways.
Group 3 are tiles that reduce pathways.
My initial inclination would be to include many copies of Group 1 in the deck, few of Group 2, and none of Group 3.
I have included a full cave tile with a 'hole in the ground" for those who might want to start thinking about a deeper cave system underneath the base cave system. Using two or more "holes in the ground" can create a secondary cave system that can be used to create a shortcut to other sides of the main board.
The 'hole in the floor' thing is something that I've borrowed from Iron Dragon, where there is a second underground railway system run by trolls. Basically, right now, I'm sort of imagining players will just simply build off the starting direction and keep going straight, with very interaction with the other players. So I wanted to create a Clue Secret Passage to get to other parts of the board.
Granted, I haven't worked out the details yet...