OK, here is an idea. If you take it, please experiment a bit to see if you get what you are after before tackling a key scene on the edge of your layout. It worked for me, but your mileage may vary, or you may just have better eyesight than I do.
Years ago, on the layout that got closest to being complete of my various attempts, there were several urban back yards and a vacant lot. I had pretty good results using tube acrylics (sold by art supply stores)- which are thick enough to trowel on with a palette knife (or a putty knife if the area is big enough). I suspect that "craft" paint of the sort sold in Walmart and variety stores will also work. I started with flat paints, and added some "water" later. You can add texture with a very fine sponge or bit of foam rubber by lightly touching the surface with the sponge and pulling straight up. Keep the surface wet by misting with water until you get the right amount of texture (the water helps keep it from turning into a lot of "points". After it dries, you can pull a dowel (hold at an angle and "drag" one end- hope that makes sense) along more worn tracks or trails- just enough to compress the surface a bit to create a well worn "trail". Build up a little thicker and maybe add some "dead" grass or weeds (late November) in the less traveled areas and against building foundations, and maybe some gravel (assuming that 25 years earlier, someone tried to dress up the surface).
If you spray over lightly with a watered down acrylic clear semigloss, you can get a bit of wet sheen, and gravity will make it settle into any low spots, imitating "puddles."
