It's not like I built an addition to the property; but I'm fairly sure that if I had made these changes as part of preparing the house for resale, I could probably deduct (nearly) all of it.

That's a common misconception. Fixup expenses in preparation for sale are not deductible, nor do they add to basis. They never were or did.

Before the law changed in 1997 you could include fixup expenses in determining how much you had to spend on a replacement residence, but the whole concept of replacement disappeared in that change in the law.

Phil
Rule Your Retirement Home Fool