Being so heavily influenced by Team Fortress 2 I think this would benefit from cleaner lighting. Try using uncompressed lightmaps (RGBA8 instead of DXT3) to get rid of the colored compression artifacts and see if you get a negative impact on performance. If not, stick with that.
On surfaces that aren't supposed to have shadows on them, like the doorway on the left, on the 39m picture, you can try if decreasing the resolution of the heightmap smooths the shadows out.