I am having anxiety about covering this lovely floor with crap modern wood :(Thank you in advance! 

We removed a rotted wood storage area and bleached/scrubbed the entire wall and sealed it.

That said it doesn't have to be brand new and clad with hand-scraped wood floors and italian marble - it SHOULD however show great attention to detail and exude pride of ownership.

If there is access to underside of its floor and it's wood I would Try drilling and spraying a few cans of Great Stuff expanding foam thru the floor and see how that works. 

Just beams of wood.

If elevated, and you have wood subfloors, a good floor guy can float out the floors to level them.

It was made out of some brick but was mostly a falling apart wood structure.  

Usually the gas company will check for leaks when they turn gas on.Never had any surprises. knock on wood...

I believe the profit is almost the same so my inclination is to sell it as is without the headaches of dealing with contractors.There are NO 3/2/2 properties in Cape Coral under the high 140's and most of those are wood frame older houses.

Previous owner didn't have a good grasp on how gravity works and removed it so he could throw wood down to the basement where he had a wood burning stove.