I tried everything I could think of. noOverlays failed to cure it. sort postProcess failed to cure it.
Finally, I fiddled with the offset settings and found that
The problem being, different values will change the likeliness of z-fighting in existing missions.
We'd need to test to see if this works better for most of the missions.
Fiasco at Fauchard St., King of Diamonds, Down by the Riverside, Business as Usual, Return to the City, COM: Behind Closed Doors, Sir Talbot all look fine.
No major z-fighting with the new value.
No Honor Among Thieves: Politics (mission 1) has some somewhat annoying z-fighting on the upper building areas
but fairly minor.
TD2: Chalice of Kings has a dirt decal on the ground that gets worse. It isn't fully cured unless you set offsetfactor to -4.