I did the upgrade a few years ago. For me, it was worth it. Previously, the saw would bog down or trip a breaker under heavy load. It's pricey and I could have bought my fantasy SawStop for the $$$. But, I've had the Shopsmith about 35 years and have the bandsaw, belt sander, and jointer. Also, space was a consideration.
I've been very happy with the decision.
If you're going to keep the ShopSmith, definitely buy the new caster kit. Wow, what an improvement.