You said "Often the value is in ones desire to think and learn".

I could not be said any better.   If you want to to figure ROI, do the math on overlaps and look at auto-swath.   That's a nobrainer for almost all growers and should be required for "green" payments.    But, the real value to GPS will be based on MidLander's statement.

I started doing VRA in 1988.  That's almost 20 years.   When yield monitors came out in 94, we first started seeing the questions on ROI come into play.   In 1995, I was working with Gary Wagner in the Red River Valley.   They had a map on their desk that showed a distinct diagonal line with a yield difference in a field that was perfectly flat and was all one soil type.   They couldn't figure it out for a long time.   And then the hired man was in the office on a snowy winter day.   The map was laying there and they got to talking about it.   The hired man said... well... that's the day you sent me out to disk, and I thought it was too wet after a while and quit, and you yelled at me.   And then the lightbulb came one.   Because these guys studied and puzzled over their maps, they learned something incredibly valuable TO THEM IN THEIR OPERATION.   They saw evidence of working  ground too wet. 

So... when you ask Gary what is ROI is... how can he answer?   Well, I did VRA and on my perfectly flat black ground, I save 75 cents per acre on fertilizer?    Or can he say:  "because I saw a map that clearly showed me cost of working ground too wet, I can now be at peace in keeping my equipment parked when the neighbor starts", and can he say that every year for the last 13 years...   You tell me... what is the ROI on that?

Ever since that trip to Gary's office, I refuse to answer ROI questions on precision ag.   If it makes you think, it may be invaluable.  If it doesn't, you are reduced to figuring out the percent of overlap you have with different size equipment in your fields.    Guys... within 5 years, reducing that overlap will be a cost of doing business.   Figuring out what it cost you to work the ground too wet... that's where winners come from.

Edit -- Might have sounded like I'm down on the guidance/auto-swath technology... If I did, I didn't mean to imply that.   My point is that there is no management involved in that decision... no more than deciding on a 60 vs 90 foot spray boom... very easy to crunch the numbers.   And in my opinion, those numbers are blatantly obvious... full time farmers need to be running guidance and auto-swath... done deal.. now let's get back to what additional things can you do with this technology as a MANAGER.