Terrific thread and how-to blog link!
I've made a half-dozen TB mats, but with acrylic sprays, and then using lacquer thinner and towels to spread and blend (or lighten) the various colors, it works, but I like your hand-spreading technique demonstrated here - and as you say - it is also immense fun painting with you hands!
Here's perhaps a tip for roads and trails I've come up with, that's pretty easy to get good results with for creating crop field furrows, trails, or rutted dirt roads - use a soldering iron to melt these features into the acrylic [plastic] mat.
1/144th scale -
20mm -