I think you were going in a better direction with your old heightmap, groovey. All the effort through tectonics and climate, and all the thought you want to put into settlements and coherent history, kind of get thrown out of the window with such a "random" process. Here's my humble suggestion: turn all your heightmaps (old and new) into grayscale layers, set them to multiply, it will get a little more chaotic and, in some way, respect the tectonics of your old heightmap... (I think). You can also try to use Wilbur (dunno if you tried it already) to get some river valleys.

As for colors, I prefer your third option. But, let me thrown in a handy pic...
homemade_ipsometric_tints.jpg
Using the colorpicker, you can make a palette with as many colors as you need.