I use CC3 and GIMP together these days, Kier.
The examples I showed above are purely CC3 maps made before I ever discovered GIMP. Here is what you can do when you use the two apps in combination:
Scribble Rock - CC3 with GIMP 07.JPG
The buildings trees and flowering bushes are all only possible in CC3, whereas it is far easier to do the soft shading on the cliffs and in the ocean with GIMP. There is a scattering of Bogies Mapping Objects around the map (boats, pier, umbrellas, benches etc) which were added in CC3.
There are only 2 flowering bush symbols in this map. Its just the colour of the flowers that varies - only something you can do in CC3 using varicolour symbols. The textures I used in GIMP to make the background are a mixture of CC3 textures (the ocean), those contained in Bogie's Mapping Objects (the sand, gravel and cliffs), and some of my own making in Genetica (mainly the grass, the rocks and the weed). The compass rose is a CC3 symbol, one from the Herwin Wielink style. I also drew the scale bar in CC3, which is easier to use when creating geometric shapes and fine straight lines. All the text is CC3 as well.
Important thing to remember...
All graphic apps are merely tools. Its what you do with them that's important