I think if you want to save some money (who doesn't) then don't test drive the Kubota. I don't mean that in a bad way by any means, but I think that after trying out (and getting used to) the HST plus, you will really like it compared to the Kioti without it.
I don't have it, and never missed/wanted it on my Kubota, but then I drove my neighbors
L5740.....
In fact, I didn't want another HST tractor in general at one time, but then learned I can get the HST plus, and I'm now back to not wanting anything but. I really like the HST plus, a lot.
I think if you never test drive one, and just go with the Kioti right off the bat, you will be happy as can be and never miss the differences. The Kioti is a great tractor in every way. Seeing that your going from 1980's technology to brand new, you will be blown away by how nice the new tractor is (regardless of what you get).
I say save yourself 10 grand and go with the Kioti. They really aren't all that much different.
If it was me however, I'd go with the Kubota.
(By the way, I do not believe in any way that you are "paying for the name" with either Kubota or Deere or any other tractor manufacturers for that matter. Also, I do not agree with most people in the importance of a good dealer, never have. Most tractors never go back to the dealer, and unfortunately, you typically spend a lot more money buying parts from them as well.)
Either way, you have an awesome predicament to be in!