anyone have any experience upping their hourly freelance rates while still being the maintainer/go-to tech guy for current clients?

I've got a client from 4 years who that very rarely gets me to do work at an hourly rate that is currently 1/4 of what I'd accept today

I want to very diplomatically either tell them their work is not worth my time anymore (unless they are willing to pay more), or to express that I can help them migrate to a different consultant

Except lately the "rarely I do work for them" is becoming much less rare, and it just gets in the way of the more lucrative (and fun!) CLJ/CLJS work that I've got coming down the pipe

I think "We have been doing business for 4 years at the same hourly rates, and it is now unfeasible for me to continue with this arrangement. If you are not able to match my current rates I will be happy to help you find a new consultant, otherwise I am sure we can reach some number good enough for both of us"

i.e. what you just told us :)

It's a reasonable thing to say. If they take offense or grouse at you about it, that's merely reaffirming the decision, sadly.