I don't play much outside of fantasy/historical type games, so I must say this didn't occur to me at all until last night, when I recalled that part of my childhood spent fooling around with toy cars.
My brother and I used to make cityscapes by using a European building toy called Majo-kit. They were intended for use with toy cars and mostly consisted of snap-together curb parts for making a series of roadways.
What I realized now, in my dotage, is that this stuff would be INCREDIBLE for assembling urban game boards! You'd still need to add your own buildings*, but you would be able to assemble a literally ever-changing urban city-scape by using a simple board with an asphalt texture (or something else to represent "street"). You would even get benches, fire hydrants, fountains, lights and all other sorts of street furniture to break things up and provide cover.
The sets are very straightforward, so you could easily make other things that fit into those little plug holes to add to the scenery options, or other things to fill inside spaces of the curbs (maybe a park section using actual grass texture, for example).
The play sets probably scale best to 15mm or 20mm, but they'll easily scale up and down and would be fine for use with 28mm figures (a few sets came with Playmobil-looking figures which may have been about 25mm?). If I ever get into more modern gaming I am absolutely going over to my parents' house and digging out that old gold mine.
*There are/were some modular Majo-kit buildings in addition to the street sets, but they're kind of naff except for the most expensive ones.
Here's some pictures for those who have no clue what I'm talking about: