Jeff - Yes, as discussed earlier in the thread, you'll get a slightly finer surface texture by sprinkling sand and sealing with thinned PVA over the top.
I never bother, because mostly in the case of my various boards, I cover a lot of the bare 'earth' up with flock etc anyway.
Also, I've always used a decorators' spray gun and compressor to paint my boards - necessitating many thin coats of paint, which tends to preserve the surface texture rather than clogging it.
In the same way, you'd need to use fairly coarse sand to get the additional surface texture - otherwise, by the time you've coated and drybrushed it with emulsion, all the texture gets concealed by the thick paint anyway.
It's going to be interesting when I get to do my planned desert terrain boards, which will largely be bare sand with little vegetation.
I'll still use gloop as a base, but will need to experiment with various 'top dressings' to get the right sandy effect...
A wash would certainly be worth a try. If you use a very thin wash of a darker colour - I mean, like 95% water with just a tiny bit of paint in it - it will run into the recesses and show up a bit more of the texture, but won't appreciably darken the boards overall. You can repeat this treatment until it gives you something you're happy with. The thing with washes is to make them really super thin and build them up to achieve the depth required. But I guess it all depends on the colour terrain you're after...

Anyway, the boards look good - it's all a learning process, eh? (And it's better than a fecking upturned Subbuteo cloth!

)