Hmm... It occurs to me that if Microbe Walls could be altered to actually *Stop* the blight, it might add a new element to multiplayer games.
Envision something like this:
This area is protected from the blight by lava flows (blight can't pass lava), and by an enhanced microbe wall several tiles thick.
The colony in the south is ready to launch a starship and escape the planet, but the colony in the north is not.
It would be in the interest of the southern colony to destroy the Microbe Wall and let the blight consume their rival while they escape. It is in the interest of the northern colony to prevent this.
There might be some potential for interesting strategies and gameplay in a situation like that.
(Also, since walls can't be built adjacent to lava, you would essentially only have the walls that you started out with. You could rebuild them to a limited extent, but if the enemy destroys a wall segment right next to lava, it is gone forever.)