Will the value of my car increase if I have installed after market parts? Eg. Body Kit, Performance Upgrade.

Buyers / dealers will opt for stock parts when buying a used car, as the modifications you have spent on are based on your personal preference. Majority of the resell market buyers will prefer a stock car over a modified car. Therefore, it is better to de-kit your after market parts to sell individually, and install back the original parts for better valuation.