Do you have a picture of your of your Neon? You did not make clear if you have a coupe or a sedan.
Your initial interest in racing aero development is for better downforce and low drag. Aerodynamic efficiency is the goal for your campaign. You mentioned it would involved different tracks with different racing circuits requiring different aerodynamic and mechanical setup. Short/Street narrow course; slow tight turns with long straightaways, requires braking cooling ducts and top speed profile. Road/raceway; wide open track with both slow and high speed corners, requires brake cooling, balanced downforce -front splitters, corner canards & rear wings. Speedways/ovals; highest sustained aerodynamic efficiency, least downforce.
The most obvious aero improvement will be the flow management over the OPEN window openings. As the airflow moves toward the rear, the missing windows create such turbulent flow and speed-sucking drag. Even if you add a rear wing, the downforce/efficiency is compromised by disturbed flow. Recommendation to have the best aero profile. Replace windows w/ clear lexan. Weld on a 'boattail' cage rails to the back with the best aero profile, cover/rivnut on lexan sheets.
Here's the recurring template for the ideal teardrop profile.
http://ecomodder.com/imgs/ideal-teardrop-comparo.jpg
Other low hanging fruit; air dam, adjustable grill block, wipers deletion, side mirrors deletion, side skirts, rear wheel covers, rear wheel spats, belly panels, rear diffuser, etc.
PS. Just for laughs, apply in uniform pattern, ball peen hammer strikes on all metal surfaces for the famous golf ball aero dynamics!!!