It's really just a matter of economics. If your C66 can be overhauled, I'd say hell yes - keep it. They do the same job as the newer version. Unfortunately, serviceable hubs are getting hard to find (if you need one) because the FAA has a zero-tolerance policy on corrosion. If you need a lot of expensive parts (or can't find parts), you may be better off upgrading.
On the other hand, some people just like to have the latest tech. In that case, call your MT dealer and I will haul your old C66 away free of charge.
C.