It makes no sense to keep trying to repair it and beating on a dead horse
Calculate the costs that it will take to tear down, clean up, and build another home based on similar projects in the area and professionals who've done similar work.
If the numbers make sense and you are fulfilling your debt service then I would see it as a no-brainer.
As a real estate agent who works in the area, I see many get turned off by unique projects like this even though it may be a blessing in disguise.
With that being said, before you make an offer, also make sure you understand what zoning is applicable and the difference between Seattle's NR1, NR2, and NR3 zoning types.
Also when building the property you will have the advantage of using cost segregation strategies to depreciate the value of certain models by 80% through the TCJA bonus depreciation law that was passed out.
If you have the money to spend, maybe get a quote from a builder beforehand.
If you have any specific questions feel free to connect with me on BiggerPockets
Happy to help,
Ran