Kubrick prices can be all over the map- if two people want something, it can sell for quite a bit more than the one before it (looking at completed auctions that actually sold).
That being said, I would say it essentially cuts the value in half for most of them, less so for others.
Finding loose examples for comparison is tricky because there aren't a lot out there. But I've been watching auctions come and go for years, and I would say most common ones from early on (droids R2, holo Leia etc.) sell for about 1/2 of a carded version. Others I have almost never seen (transparent Han carbonite, holo yoda), so those may stick closer to 3/4. But they all definately take a hit.
If you wait it out, you may be able to find loose versions, then sell your carded ones. But you'll be competing with me for a few of the loose ones