Idea: Instead of concrete for all tiers, use landfill for the simple tier, stone (if that's in vanilla) for the residential tier, and concrete for the highrise tier. Landfill is what cells would start with, and as houses are upgraded, the tiles are replaced. The range of upgrades should probably not be limited to just the house's cell, but one or more cells of range around it.
Don't downgrade existing streets, just use it for new ones.
Based on https://github.com/bahrmichael/factorio-tycoon/discussions/287#discussioncomment-8938407
Idea: Instead of concrete for all tiers, use landfill for the simple tier, stone (if that's in vanilla) for the residential tier, and concrete for the highrise tier. Landfill is what cells would start with, and as houses are upgraded, the tiles are replaced. The range of upgrades should probably not be limited to just the house's cell, but one or more cells of range around it.
Don't downgrade existing streets, just use it for new ones.