I am a 22+ year owner of various Transparent cable levels. I concur the jump from Super to Ultra is quite noticeable, especially when going to Gen 6.
What I noticed immediately what appears to be more bottom end, and better overall separation across the entire frequency range. I use both speaker and interconnect for analog connections.
As far as upgrade I have always been given a resonable trade in when going up from one series to the next. Try calling them or work with your local dealer which is what I always did. Do not remember the exact percentage but I think it is around 70% of what you originally paid plus the difference from one series to the next.
Also, I think Ultra may be the point of diminishing returns but I was honestly blow away by the improvement and expectation bias does not factor in. The difference is easily heard even by casual enthusiasts.