I've been deleting a lot of duplicates recently. So here are a couple of ideas to stop this trend:
1) When someone adds a module, look-up the name / manufacturer added and if there's already a module with that name (yes, I know variations can exist) then suggest that the module MIGHT be a duplicate
2) If a duplicate of a module exists and is being used then add a warning (similar to the incomplete power info warning already available) saying that user is using a duplicate module and that they should revert to original version
3) Do a purge. Seriously, let's clean up this place of all the damn duplicates. They will get removed from peoples racks, so be it! I can't believe I have to hide modules which are the reverse panel of the original, which is already available as an alternative to the original module by scrolling the Panel Selector options.