I don't think they help noticeably, but Hartmut Feyhl from RENNtech specifically stated that his cars saw a gain on the dyno with the vented panels; however, that's on a 6.0 litre motor with aggressive cams.
I think this is primarily an aesthetic modification, so do as you please (I like my Stainless Steel mesh, which is a clear Bentley ripoff). I do recommend you use some sort of screen on the backside to prevent sucking in big chunks of debris.
Good luck to all
