If you think you need a rear wing, ask yourself,:
Why?
  • How much will it cost?
  • How will you adjust it?
  • How will you test it to know how to adjust it?
  • Will you use a wind tunnel to derive the best height and attack angle, and the relative positions that yeild better drag or better downforce for the different tracks you run?
  • Do you have on board data aq to help make those track to track calls?
  • Have you developed every other aspect of your package?
  • Do you have the budget to replace the springs you'll need with the new downforce?
  • And the dampers to go with the new springs?
(Oh, and the original allowance of "air dams" was probably done so as to create a logical place for brake ducts to mount to. Air dams were common at the inception of IT)