Just my opinion, but if the original house had 1,500 sf, and they are pricing it basically as a 1,500 sf house, it shouldn’t be much of a problem for you. Since you’re buying it at a “discount” from 2,000 sf houses, you’ll simply sell it with the same type of “discount” when you sell it. Nothing lost, nothing gained.
In the meantime, if the addition looks like it’s in pretty good shape and a qualified general contractor can take a look at it and tell you that it would be easy to get it permitted, you might be buying it at an actual discount because you could get it properly permitted and sell it as a ~2,000 sf house if the addition is done well.
Yes, neighbors can complain, and there’s a chance you would have to take it down, but if it hasn’t happened yet, there’s a good chance it won’t happen while you’re living there.
