If something is "rare" then I'm always inclined to keep it. However, "rare" doesn't really exist much anymore.
Limited Edition Modern Warfare bundles are still on store shelves.
Even those Limited Edition Halo 3 Master Chief helmets can be found in stores.
I agree with Failed that the GoW Trilogy may be sold out today ... but probably won't be sold out for long. As long as people are buying them, the publisher will keep making them.
Unless you are an avid collector, I suggest selling the bundle now, and then buy the bundle in a few months when they reissue it.