The Pass 30.8 is a very nice amp. I have not heard the Carver but I own a ARC Ref tube amp. I can tell you that Power tubes will not last 50 years. They will last 2000 to maybe 4000 hours, it depends on the tube. Signal or small tubes will last much longer. There is more up keep and maintenance for a tube amp. Is the amp auto bias or do you have to bias it?
I don't normally buy anything without hearing it in my system. A good system needs synergy. You can't just buy two well reviewed components and hope they will work well together. You need to hear how it sounds in your system.
What is the rest of your system? At the level of your amp it could be a sideways move. Different but not necessarily better. I doubt the amp is the weak link in your system. If you want some tube "magic" you might want to consider a tube preamp first.