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...
You can improve your ship's capabilities in the garage, using funds accrued from race wins.
Faster ships are unlocked as you progress through your career.
Some tracks have multiple routes - keep your eye out for potential shortcuts.