It's really important that everybody thinking about this topic understands that there are two very different considerations to insurance on a tractor. The first, is replacement insurance. As was mentioned, most of us could recover finacially from "self-insuring" our equipment if it were lost or damaged. Whether it's a $12,000 subcompact or $30,000 utility tractor, we could somehow find a way to put beans and bread on the table.
However, the second consideration is liability. Unless you guys are incredibly wealthy, liability self-insurance is a fallacy and could result in a loss of everything you have now, and everything you might earn in the future.
I know there are a few insurance agents here at TBN, and their sage advice would be to talk to your agent--period. Laws and policies vary so widely that no one situation posted here would ever be a safe answer. I have a little over $25,000 in outdoor power equipment, including a $13,000 sub-compact, that IS covered under my homeowner's policy for loss, damage, and liability. My use of the equipment IS covered anywhere I use it as long as it's not for profit. The accepting term in my policy and in the letter from my agent is "...non-commercial property maintenance, on or off the insured property, operated by the insured."
Don't forget, it's the liability issue that is the real "killer" here.