I can’t help you with Denver. It’s been nearly 7 years since my last visit. Although unless things have changed, my first “off the plane” meal in Denver would still be Buckhorn Exchange. That’s about as “Iconic Denver” as you’re going to get.
My last visit to San Antonio and Austin was back in 2012, not too long ago. In Austin I’ve never been to Threadgills and honestly have no desire to visit, I’ll always go to Hoover’s. I really enjoyed J Mueller in Austin, when I was there he had a trailer, if he’s still there I’d check it out
In Lockhart, Smitty’s…..Period…..
I can’t really help you out with San Antonio since you’re not into Tex Mex, although for a “bean burger” I’d check out Chris Madrid’s