If a paved tile has not had a player within five tiles of it for some certain amount of time, the tile gets growth of plants and eventually gets destroyed. If a player walks over any tile within 5 tiles of overgrowth on stone tile, the overgrowth dies. Maybe a rare curio that requires high per * exp in old almost decayed paved tiles.
Buildings may have overgrowth if the hp on building is below 75% and has not had a player within 2 tiles of it. Buildings below 25% hp may start to visually cave in on the outside (roof fallen in), and on the inside it is similar to a cave in, but with planks or something instead of boulders. If furniture gets hit by rubble it immediately gets destroyed.
With plowed tiles, its the same as paved tiles. If there is a crop there that is not harvested for 2 weeks, it becomes a new item called "Moldy Mush". The crop itself visually would just be tinted yellowish. Moldy Mush at q10 gives 1200 lp/h with 4 mental weight. Functions as high tier curio for anybody who stumbles across ruins. To negate botting, it decays after 1 hour of harvesting. The actual moldy crop decays after 3 hours of becoming moldy to make hitting even more difficult. Another possibility would be to make it an only 50 or 25% chance to even get moldy mush.