I think you are going to enjoy both purchases.
I (and several others here) have the Carter stabilizer, in fact I have one for other bandsaw and for my shopsmith. If you want to do some fancy scroll work this is the way to go. I have the other guide block set from Carter on my other bandsaw and that was a major improvement for that saw.
The other purchase, if you liked your old shopsmith then you will love the new one.
As for the older one, if you have room keep it. Do a rebuild as needed and then you will have a backup machine and remember it still has those 5 functions it started with so you can have each machine available for any project you might think up.
I was at the New England Woodworkers Show this past weekend and purchased a Carter Band Saw Stabilizer. I am hoping that they are half as good as the demonstration! Oh, and across from the Carter booth was the Shopsmith booth. Great demo on the Mark vII.
Had not planned to buy one, but the tool gods were calling to me. Should be here (with a "free" dust collector) in a few weeks.
Much improved over my 1982 all original Mark V. Not quite sure what I will do with that, but the bearings are howling...