In all the talk of graphical downgrades no one seems much preoccupied with 'why?'. Why build something and then proceed to tear it down, piece by piece, in the hope that ever more diminished expectations about the final product won't be severe enough to...
Go for the Space Tiffin on every level, for you'll get extra points and a power boost.
Focus on the green and red blobs - those are the ones you need to kill to finish the level.
You can shoot the triangular walls that get in your way.