I also own a Trackball Explorer 1.0.
If I had any inkling that Microsoft was going to quit making these things, I'd have bought as many as I could to have a supply of fresh trackballs and potential spare parts.
Everyone I know who has owned one has said the same thing: it was the best, most comfortable trackball they have ever used.
As it stands, I'm sending mine to a reputable shop for refurb and looking to purchase another used one to get that refurb'd as well.
I think many people would gleefully buy a modernized version of the Trackball Explorer. I wish Microsoft would start making these again or even sell the design to another company, like CH Products, CST Microspeed, or ITAC Systems.
I would buy a baker's dozen, just so that I never go without one again.