You are absolutely correct, SSD's do have a finite amount of write capacity and SpinRite will lower that due to it's very nature, at least 6.1 will. However I think you are over estimating the amount of wear it will place on the drive.
I understand the objection and it's a valid one. I have used it on my boot SSD to restore it's performance to great effect, do I recommend using it every year on a SSD no i don't.
As this post is mostly about data recovery, I still believe it's a valid option and the performance increase is just a nice bit of bonus information.