Now it looks too simple, but at least it looks much better. It's difficult to tell you exactly what you need to do for it. IMO, this looks better than the first back end but also its too simple. Think diffusers, you need a rear aero lip, vents for rear brakes, a license plate holder, maybe some extra chrome bits, and stuff.
If you need more ideas, check out
ManHell Automotive. Razyx is a power house when it comes to fixtures.
Of course you can leave it, it looks fine but just... kinda bland. Some sports cars IRL are like that.
EDIT: Also I'd like to see some stats

This might also be a competitor for the Aeroline Mongoose. Would like to see a sports car auto magazine with our cars in it! ohhhh utopia.

Mongoose vs. Fleetwood vs. Canyon... YES!