Is there a point of diminished returns with amps and Harbeth 30.1s?


I’m currently using Herron M1As with my 30.1s and I’ve upgraded the rest of my system (Aries/Fatboy/SUT/DL103r and Lamm pre and phono) and each upgrade has been VERY satisfying. So is it going to be worth spending $5000 or so on the used market to upgrade the Herrons? Any thoughts as to whether I’ve reached the apex of amp/speaker performace for the M30.1s?
dhcod
An easier upgrade route might be to sell the M30s and buy the M40s.

Few would argue it's not a clear upgrade.
Thanks and sorry, I should have mentioned that I’m stuck with the 30.1s due to space limitations that require me to move the speakers in and out each time I listen. I will buy the 40s in a heartbeat if we ever move!
Put the turntable on Townshend Pods (or Platform) it will be a huge upgrade. Put the speakers on Podiums, if you can. Might not be convenient if they are moved around a lot. Synergistic PHT and ECT on the turntable, HFT on the speakers (and walls, if possible) and ECT on the amp and other electronics.  

Do all these the improvement in detail, dynamics, truth of timbre and imaging will have your jaw dropping in amazement. You will forget any thoughts of "diminished returns" and be trying to figure out what else you can do. When that time comes PM and I will hook you up.