This is why any potential AirB&B purchases should also work as a normal rental. Municipalities are under pressure from the hotel industry to ban AirB&B's, and even if a location is currently legal the laws can change.
City's don't care if you have the biggest, nicest, bestest home in the area, but they do care if you are running an illegal business with unpermitted construction, and torked-off neighbors complaining won't help.
The reason you are their focus is that cities are always over budget and looking for money. Hotels usually pay high local taxes and employ a lot of city citizens who also pay taxes. Add to that the unpermitted addition that no property taxes are being paid on and the city is going to take a real disliking to you.
If you sell, keep in mind that appraisers often don't assign any value to unpermitted square footage. In many states, tenants can sue a landlord for renting an illegal structure. I would also ask your insurance agent if you are covered if someone is injured in a non-permitted addition? Eventually, a sale or the government causes the unpermitted additions to bite the homeowner in the butt.
As always, seek professional advice. Good luck.