Personally I think the pollution problem can be addressed quite easily. The rules can stay the same where the pollution forces resources to reallocate BUT the game engine could be smart enough to reshift resources back to the polluted square if the square was previously be used as a resource. I have noticed some kind of intelligence in the game engine in that the game will choose the most productive squares and what not. If pollution was cleaned and that square is more productive than another square, then it shouldn't be a problem for the resources to shift back just like they were originally shifted when the pollution appeared. That's my 2 cents.