I have Forte, Forte II, Heresy II, KG 4.5 and Quartets.
I love the Quartets! (Disclaimer: I love all of my Klipsch speakers.) I agree with all you've stated in your post, and will never part with mine. I do have the Crites Diaphragm upgrades in them, and highly recommend you do this very easy upgrade. The crossovers will also be done soon.
During my Forte II upgrade I used them as my mains, and had nothing to complain about. Smooth and with an excellent sound stage, they worked flawlessly.
They now are part of my 7.1 system:
Forte IIs mains
Forte I rear-surrounds
I'm temporarily using an RB-61 for a center. Being built is a custom center consisting of Forte I mid and tweeter, Forte I crossover and an 8" woofer with perfectly matching Theil parameters to the original K-23, including SPL. It will be ported and fit in the center of my TV console.