Most online reviews say that RX11 is not much of an improvement over RX10 and it's not worth the money.
I watched a video highlighting the difference, and the only thing that even looked interesting was to be able to view/edit the spectrogram in mid/side mode.
I tried it out hoping that a small bug I found in editing has been fixed, and was disappointed to find that it has not been. I can't even find a way to tell anyone about the bug - online reports say the support email is no longer working, and I couldn't find any reporting forms. Some speculation that the company is not really putting any more effort into improving the program.
Spectralayers Pro 11, however, seems to be a large improvement over 10, and looks like it may be a good replacement / alternative for RX.