I think DMZ has a good point about condition.
A story from this week that kinda relates to the OP. While out doing a couple of rural land appraisals, a homeowner asked me who I was and what I was doing etc. I told him I was an appraiser appraising the adjacent land, but that I couldn't tell hem much more than that. He proceeded to tell me more than I wanted to know.
Anywho, the intersting thing was that he had purchased a lot in this subdivsion (+/-10 acres each) that had an old house that was basicaly a tear down and had rehabbed it, he had pictures of it in the before condition, and I had seen it before as well. If I had appraised it in the before condition, the cost to demolish would have offset the value of a typical 1 acre site in the area, resulting in a $0 value in theory (if it was on a 1 acre site). He purchased his 10 acre lot with a discount of the demo costs of the house but didn't demo it, he fixed it up, utilizing the value that remained in a house that most folks would agree appeared to be dozer bait. The contributory value of what was left was certainly much more than the cost of demolition, so did the improvements really have negative value?