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
Had one. Hated it. Exactly the opposite of the sound I enjoy but that’s just my ears.
I know you are asking about amps, but IMO, contrary to Alan Shaw's opinion, speaker cables make a big difference.  I've owned the M30s, SHL5s and P3s and I've found the right speaker cables to improve the sonics significantly.  I don't know what you're using now, but if you have to move the speakers often, I would see if the Cable Company has any more Audience AU24 show demos at 1/2 price.  Excellent sound and very easy to work with.  I also love Purist, but they are not the cables to be moving around on a regular basis.  Not that you can't, but they are kind of bulky compared to Audience. 
I would see if the Cable Company has any more Audience AU24 show demos at 1/2 price. Excellent sound and very easy to work with.
FWIW I have used AU24E with my 30.1 all along, and have been quite happy.
Thanks for the suggestion re: AU24s. I use the Audience Ohno already. While there may be a big difference, it would cost an arm and a leg because I need 5M runs. Seems like the best money is still to be spent on an amp.