I'm with Dave on this too, the selling dealer makes a decent % on selling the certified warranty, and its not the dealer that takes the hit (for a claim) its the company and the dealer gets reimbursed for the repairs .
We extended our warranty an additional 5 years on a car with a lot of spendy stuff to repair even tho it's been reliable, and got three prices (same plan from three dealers) that were $3100, $3400 and $3900 - we went with the middle price from the original selling dealer at the end of the day.
I did this for several reasons, 1) a repair today on any major component - suspension, transmission is $2-4K, or a minor component is $600-1200 2) the car has been under bumper-bumper warranty since new, so for a prospective buyer there are no major issues that are hidden/not repaired 3) If we elect to sell it the warranty is transferable and in the end should bring more value to the unit.
I would buy it and if you use it, with the history you have had, I would probably trade it in 2 years if you can afford to, as having that may issues with a tractor doesn't bode well long term.
Carl