What felt incredible was getting the setup and prompting right and then producing reasonable working code at 50x human speed. And you're right, that doesn't excite after a while.
But I've found my way to what, for me, is a more durable and substantial source of satisfaction, if not excitement, and that is value. Excuse the cliche, but its true.
My life has been filled with little utilities that I've been meaning to put together for years but never found the time. My homelab is full of various little applications that I use, that are backed up and managed properly. My home automation does more than it ever did, and my cabin in the countryside is monitored and adaptive to conditions to a whole new degree of sophistication. I have scripts and workflows to deal with a fairly significant administrative load - filing and accounting is largely automated, and I have a decent approximation of an always up-to-date accountant and lawyer on hand. Paper letters and PDFs are processed like its nothing.
Does all the code that was written at machine-speed to achieve these things thrill me? No, that's the new normal. Is the fact that I'm clawing back time, making my Earthly affairs orderly in a whole new way, and breathing software-life into my surroundings without any cloud or big-tech encroachment thrilling? Yes, sometimes - but more importantly it's satisfying and calming.
As far as using my brain - I devote as much of my cognitive energy to these things as I ever have, but now with far more to show for it. As the agents work for me, I try to learn and validate everything they do, and I'm the one stitching it all into a big cohesive picture. Like directing a film. And this is a new feeling.