I don't "get" the game either. But my kids (7 & 8) adore it, and they are constantly building race tracks and games for their Guardians of the Galaxy figures to play in.
I'm not too bothered about not getting it, but I harbor deep hope that the Star Wars packs in Disney Infinity 3 can finally prod me to fiddle with the Toy Box and unleash the awesomeness that is hidden away in there.