I would definitely stick with the PMC's for now.
I don't see much point in making relatively small, incremental improvements to speakers - which would seem to be the case from your lack of confidence that the Kef's are hugely better. I would want to wait until I could afford a dramatic change. The only case I could see for spending on incremental improvements would be if this were offset by a future, dramatic decrease in the current, second-hand value of your PMC's.
If I were paying new money then I would also try and find a dealer who would let me have a home demo. Maybe your dealer's also not that confident that they would be a substantial improvement.
In the meantime I think I would learn more about the acoustics of my room and what it could handle. Maybe analyse your room using REW, try and borrow different sized speakers from friends, or even try and arrange a 'bake-off' with members of a hi-fi forum.
Perhaps just a new pair of stereo, floor-standing speakers could be just what you need. But also try and take a long-term view in regard to your whole kit working together, not just the speakers. Sometimes it's better to take a completely fresh approach rather than making alterations here and there. For example you might come to decide that a better overall solution would be to introduce room correction, and/or maybe some very-well integrated subwoofers, perhaps using active crossovers, and perhaps stand-mounts rather than floor-standers. Or maybe some active stereo speakers. I appreciate that you've already invested money on some expensive electronics but I would presume that they have a good second-hand value that could off-set the cost of something like a new amp with superb, built-in, room-correction and cross-over. This is relatively new technology, which I imagine will become more affordable than current products such as Lyngdorf.
What is it that you find unsatisfying about your PMC's?