I've downloaded MathMap, but don't know when I'll have a chance to play with it. For those who would like to play with textures here's an algorithm that you might try.
Values of md below 1 will flatten lowlands, making lowlands flatter and highlands more spikey. Values of md above 1 will raise highlands, making highlands flatter and lowlands more crevasse-like. Note that the working equation preserves the range used, though it will leave gaps.
set st = !lowest pixel value to modify!
set fn = !highest pixel value to modify!
set md = !exponential modification!
for each pixel valued from st to fn
set v = !starting pixel value!
set !ending pixel value! = ((v-st)^md*((fn-st+1)/((fn-st+1)^md))) + st
For erosion, two things occur to me. First the algorithms may not work when you're dealing with an area that isn't completely affected by water. Second, the 'weakness' of an area may need to be taken into a account. Block an outflow with salt and water will eventually it wear away no matter how steep the incline involved. Possibly this could be handled by generating a second texture for the relative strength of the terrain.
I will take a look at Wilbur.