Nice tiles Torstan,
My advice to make them more "interchangeable" but not to have the grid pattern is to turn some buildings on an angle and also to not fill up the entire tile. That helps to make a bunch of square tiles work better together to create a varied output. The fewer parts that are built out to the corners will break up the pattern easily.
The other idea is to make the square tiles free and sell rectangular ones. They could contain more buildings or just simply buildings that span the center to really break up the pattern of squares.
Of course if they are interactive to change the color of the things you only need a couple dozen and you have a whole city!