Coinneach,
I disagree, he's talking about sticking them in a safe. So far as I know, you can "buy back" (actually a misnomer, whether a govt entity does it or a private individual, I digress) all the guns you want if that's what turns your crank. If you start selling or trading in any volume there might be some issues, but buying and collecting isn't regulated by volume (yet).
I'd check state and local laws, but I wouldn't hesitate to go for it. As I mentioned, you might just get really lucky.