I would like to think of them in Time Crystals. If the buyer needs to build something different, that change cost 50 Time Crystals. A common natural Plot that has been cleared should be valued $10 - $15 more. It's not a perfect number by any means. 80% good is good enough for me to make decent decisions before diminishing returns of extra number crunching kicks in.

PS: Now I think about the edge case where extra number crunching reveal some useful insights that can multiply ROI. Then I think about how many smart people are crunching numbers and how long such a thing could remain unnoticed. There is going to be someone to write about it open source it!