The export feature saves sequences of only 2 identical bytes with the escape byte, ie. it basically "compresses" 2 bytes into 3, thus making the caves bigger than necessary.
I think the way you implemented the Maze and RandomFill is okay. As you don't have fully implemented the Levels attribute yet, I wonder about one thing. I assume the engine will expect as many seed values as there are levels, right? This is a very important detail which has to be documented in the BDCFF specs.
And will you support Replace_Element in mazes too, so that none rectangular mazes will be possible? (Which is actually possible in Crazy Dream 9 already, although I only made use of this possibility in the title screen)
Alternatively, we could use a Maze_Auxiliary element instead of a Replace_Element and grow the maze in the way Crazy Dream 9 does. This might be a bit easier to implement, but also less intuitive for the cave designer, so I still would suggest the Replace_Element. Should be even feasible on a C64, I think.
I see, you fully support Crazy Dream 9 now, which certainly isn't a bad thing as such, but isn't it against your "will be tweaked manually"-policy?
Your bias parameter in mazes has no text in the setup dialog. At least not in the German version.
And I don't think that "Labyrinth" is a good translation of maze. It's the same as in English:
http://en.wikipedia.org/wiki/Labyrinth
See also Labyrinth in Daedalus for details.
"Irrgarten" is the common term for "maze" in German.
And yes, those are often confused indeed.
The NONE element is a good thing, we should document in the BDCFF specs as well.