In the wrapper used to be fairly common. I haven't heard of anyone collecting GG mags. I think that there were only two or three manufacturers so there isn't a lot of variation to make it interesting.
In the wrapper it should be in like new condition though there may be some off color or surface "issues" from the manufacturing chemicals (bluing or phosphating). I'd say that they are worth a few bucks more than a new condition that is not in the wrapper but of course you have to find a buyer which will depend on what you are asking for it.
If it was me I'd rip it open and shoot with it.