What equipment should I invest in next?

Demo  a Power Plant. You'll only be out shipping if you don't like it.

Very nice system as it stands! Get a cheap Schumann Generator.

First thought is that you are thinking in the right direction - cleaner power.
Regenerator or not, better power cables perhaps...
I use older PS Audio regenerator.
What does your turntable sit on ? Yeah, that's another direction - vibration control/tuning.
Put one half inch Walker Audio resonance control disc near your turntable motor, see what difference it will make. I heard slight but obvious improvement with my Nottingham. I got it directly from Walker for $50.
Perhaps another disc on top of SACD transport. This I don't know but I had the same effect as with turntable with the disc on top of Nakamichi deck.

Based on what you said, Townshend Podiums. I've used all kinds of power conditioners, power cords and cables. Good ones will definitely make a big improvement. But you know from first hand experience the unique timbre and tone of live instruments. What you are hearing right now, I'm sure it sounds very good but let's face it, you would never confuse it with a real live instrument in the room. Even my Moabs as dynamic as they are, we just don't get there.

But then even if we had the incredible dynamics of the real thing, we would still have the problem of the real thing starts and stops. The overtones and resonances we hear with a real instrument are produced by the instrument itself. The musician holds the instrument perfectly uncoupled from the floor. Piano and string bass, some drums, are among the few that couple to and excite the floor- and more and more pianists are discovering the improved sound of putting the piano on Pods! Search YouTube, watch the videos! 

Speakers on Podiums will do something for your music no conditioner can: restore truth of timbre! I have no doubt you will hear this immediately, and probably be surprised at how much instrumental uniqueness was hidden in those colorations.