1) I think it is an artifact of mipmapping, which causes the texture to become more blurry far away. See if disabling mipmapping will take care of the problem.
Code:
grid.appearance(viz.TEXNEAREST)
If this doesn't help then you might just need to make the grid a brighter color.
2) You are probably importing objects in the global scope of your module and importing the module before you call viz.go(). Remember that you can only add objects after viz.go() is called. So try importing your module after viz.go()