The aero on the car is critical for its performance. On the Spoon Sport Civic It is simple but correctly done to standard common sense guidelines for basic aero design. The aero does not hint of signs that it was done using CFD or windtunnel testing but everything is basically done correctly.
The rear diffuser starts at the rear axle centerline which is common across many rule sets. It has a kick up toward the end that exceeds the usual maximum of 10 degrees before flow separation typically starts but aggressive vortex generators probably help keep the flow attached in the kicked up rear section.
This diffuser extension plate behind the rear tire probably doesn't do a whole lot as it is in turbulent flow but it probably contributes some downforce and might have some effect on the wake. The rear canards are probably mostly for looks but help a little and probably don't have much of a drag penalty.
The side skirt has a stagnation plate in front of the rear tire to create some pressure differential on the side skirt. The side skirts are well designed with extensions and side plates to reduce spill over which helps pressure recovery. The skirts hep prevent spillover air from the top of the car from curling under the car, messing up flow to the diffuser.
The extensions, stagnation and side plates make cosmetic side skirts highly functional. If your rules allow, check this out and take note if you are looking for ideas on your own car. This stuff works, won't hurt and is not that hard to fabricate.
The metal rear deck is removable with a smallish 5zigen wing used for trimming the rear downforce. The wing helps make the diffuser more effective by helping activate the flow through it. The wing was trimmed down to a minimal angle of attack for the last event.