Hello,
I feel your pain. When I first shopped for a tractor, I went through some of the same pangs of uncertainly that you are having. However, I bought a Grey Market Yanmar, and now I feel that it has been one of the best purchases of my adult life.
I was careful to pick a solid unit. I maintain it well and I have not needed to fix it. However, from the research that I have done, I feel confident that I can get most of the parts that I may ever need. Buy a good solid tractor from a reputable dealer who will help you fix it. If you decide to do something stupid and break it you will have someone who is knowledgeable with the tractor to help you.
Your friendly Kubota dealer has an agenda. If he sells you a tractor he makes money. If he needs to slam the Grey Market dealers to make a sale and twists some facts in the process, well let him do so. Some Grey Market Tractor dealers will tell you anything you want to hear to make a sale as well and the truth may suffer. The REAL truth is often somewhere in between. There are a lot of satisfied owners of Grey Market tractors in the USA like me who have saved thousands of dollars. I would not do anything different. Tractors are a great tool and a bundle of fun to play with, but to me I refuse to spend the better part of twenty grand for a new tractor.
If you need any more info, email me and I will try to give you the straight scoop.
Thanks,
Cameron