I've done a bit of experimenting using simpler cloud-fractal hoo-hah for overall arrangements but then using DEM overlays to bring realistic definition to the upper elevations. Not much to report so far (too many other projects distract me, and I have no actual use for it beyond fascination), but the mutant beasts which have resulted do show some glimmers of promise.
I guess the main difference between what I've attempted and what you're working on is that I don't cut-and-paste fragments ... I combine complete DEMs with complete random hoo-hah in an automated routine which forces the DEM data to dominate the upper elevations while fading in prominence as they approach the waterline (and all submarine data is left randomized without DEM additions).