Gurney flap (wickerbill) is small, then you get spoilers and then wings. Each function differently.
The turbo New Beetle had an active spoiler built into the top of the hatch. A wickerbill would be appropriate on it's trailing edge. It's kind of a spoiler on the spoiler.
A wing creates downforce, while a spoiler is basically a vortex generator.
You might want to review this thread:
ecomodder.com/forum/showthread.php/aeromods-2001-vw-beetle-19668.html
Julian [banned] Edgar made a similar wing with transparent side plates, but he only has four other threads remaining so it must have been in some other thread. It might be in his Autospeed pages.
Minimal:
ecomodder.com/forum/showthread.php/aeromods-2001-vw-beetle-19668.html#post274074
Maximal:
ecomodder.com/forum/showthread.php/aeromods-2001-vw-beetle-19668-2.html#post324256