you need to take into account that all the changes were an improvement from one version to the next. Shapeoko is now on the fourth generation.
X-carve was a fork from the Shapeoko-2 and now is on the second generation (there was improvements from the first but not a complete upgrade so we will call that version 1.5)
so as far as what is worth is a personal decision, what do you need, what do you expect, and what are you willing to spend to upgrade.
will this be a starting point from which you use to learn and grow or will this be a final purchase in which you expect certain performance functions without any other expense?
keep all of this in mind as you move forward. you can get a feel for what you can give from accessing this information.