Speaker upgrade question.

Hi all, 
I haven't been here for quite a while as I've been happy with my KEF Reference Three-Twos driven by a Musical Fidelity A308. They're both vintage but they sound great together and fit my somewhat weird room. I'm pondering spending some bucks in the 3-6K range for new (used) speakers and I have a few questions. Thanks ahead of time for anyone who's not too busy to help.
First, would I be  upgrading beyond what my amp is capable of keeping up with? The MF is fairly powerful, but I'm not sure of its limitations since they don't show up in my current system.
Secondly, how high up the price ladder would I need to go before I'd find speakers that offer an obvious improvement over my KEFs to most ears. There would be little point to pony up money for a comparable sound, however much I subjectively prefer subtle differences.
Finally, for reference purposes, can anyone tell me how the following modern speakers might compare or contrast with mine? (Some aren't in my price range, I know) Triton 1R, Kef R7, comparably priced Monitor, Revel, Gato, Paradigm, etc. I wouldn't mind a bit more punch and a bit more bass than I have now, mostly just to experience a different sound - I respect the KEF signature sound.
I know that sometimes it's hard to accept the premises of these types of questions since such matters are so subjective and a lot of folks like to lobby for their favorite brands. I guess I'm not seeking advice about what to buy. I just want to understand the benefit to me of more modern speakers. It's quite possible it makes no sense for me to upgrade.
Thanks again.
Marc