Started by throwing out the old levels, starting over is both scary and refreshing:
I wanted to do a easy tile editor, each tile is 8by8 blocks in size
First trial to use the tiles on the world
Added roads
Made it generate random terrain models
The ground was too flat so I added a noise map
Made it put different materials on different heights
Roughed up the road by randomly adding blocks at the road edges
Used a similar trick to make the walls look less sterile
That was the easy part - redoing all the old levels is going to take a while.