I've already explained what I like about Kandor. And as long as it remains in a bottle, it works for me. But I would fix the problem of them actually having survived. They haven't. They are all dead and they are just living an illusion of life in a small bottle city. Brainiac simply harvested their bio-patterns to observe them in a simulated reality.
Superman knows this and can enter the city (somewhat like AVATAR) by using a simulation of himself in Kandor. But he never lets on that he knows they are all dead and simply computer created ghosts. Didn't Captain Picard have an adventure like that on ST:TNG? I think this might have given me that idea.
It's good to have different realities that Superman can enter and have adventures inside. And it's good to explore and expand the fantastic world of Krypton.
What was boring about the Byrne Superman and the 1940s Superman was that Superman was too bound to Earth and mundane reality all the time. Fletcher Hanks seemed to recognize the potential of Superman better than his own creators, as Stardust the Super-Wizard had the kinds of way-out adventures that Superman ought to have had but didn't back during his original decade.