This has been a war tactic since Alexander vs Darius times. I think we should be able to plunder our own tiles (using combat units). Maybe without getting the HP and gold boost. That way we can deny our enemies the plunder, while at the same time keeping our improvements for later repairment (crucial for GP improvements). We already get a happiness hit from plundered tiles so in that regards it seems fine. Obviously the people working the farms would be kinda upset when their allied troops destroy their land. Now I play on quick so workers removing improvements only takes me one turn, and if that's the case with other speeds then this feature seems for the most part pretty pointless. However if workers can't one turn removal, then it may be a useful tactic if you get hit with a surprise attack.