Fun zombie thread!
This is actually a great one to revisit. I think modernist design was still generally reviled in 2007. But that was also the year Mad Men started. A few years later everyone was obsessed with barbers and midcentury modern furniture. Our perspective on and appreciation for 20th century stuff has changed a lot.
This hasn't always been good. There's a lot of objectively bad stuff (or, at least, stuff that doesn't work and is recognized as failure by most; most including the designers themselves) from as late as the '80s getting listed as historically relevant and, therefore, forever condemned to failure.
I don't want that to happen to places that would like to grow past being car-dominated failures. But maybe they've had their chance.
Anyway, I nominate:
Milton Keynes
This is what I mean about protecting something bad. Still, it's extremely 20th century. Let's dunk it in resin.
Bartlesville Oklahoma
I don't understand why Bartlesville is the way it is and I'm not people from there understand either. Still, Frank Lloyd Wright tower, Taliesen "Community Center", solid collection of substantial early and midcentury buildings, lots and lots of parking. This is a 20th century place.
Coventry
Nothing quite as 20th century as getting bombed flat and rebuilding as a car-centered dump.
Dresden
Except maybe getting bombed flat and rebuilding as a communist dump with fake historical buildings.
Katowice
The Polish have been building glass towers everywhere lately, kind of ruining the effect of communist city planning without making it better, but Katowice is still a nice example.