I moved from an RB-1080 to a Bryston 4BSST. How much of an improvement did I expect? Well...a little...you know, diminishing returns and all that once you get to a point.
What did I get?
A MASSIVE improvement in absolutely everything. Forget diminishing returns, this was huge returns...the treble is extremely refined now, the midrange is smooth, and the bass is accurate and well defined (versus the Rotel's "look at me I can produce bass").
My new Martin Logans (

) aren't here yet, so I'm still running my Energy Veritas 2.1s (~$500USD used), and even on those there was a HUGE difference.
Don't get me wrong here, Rotel still makes great gear, it's just not at all in the league of Bryston.