Something as simple as using a thin mix of a suitable colour craft acrylic on the sand gives it depth, and helps it look the part.
The base lets an otherwise good model down.
Awesome look to the Lava Plates. As for the basing, WAY back in the RTT days of "That Other Game", we either made them look like this, OR sand/grass covered the WHOLE base. Everyone was standing on 8" tall round hills.... Looks Great!!