If you're 100% sure that you want to keep them forever, then go ahead and open them. Aside from losing the seal, they won't degrade if you take good care of them.
The thing to recognize is that unsealing a Magical Chase is essentially a one-time, momentary indulgence that is worth thousands of dollars. A couple of those other games are up there, too. If it's worth that to you, then great, you just got a f*cking fantastic freebie. If it's NOT worth that to you, however...if in fact it's not even close...then you should locate someone for whom it IS worth that much, sell it to them, and spend the cash on an indulgence (or a necessity) that is worth that much to you. There's no shame in not being that hardcore of a TG16 fan, no matter what anybody says.
In my case, I'll come right out and say that I'm basically poor, and the thousands I'd get from selling that haul would be life-changing enough that I'd feel irresponsible not to sell it. Then again, I'm not the hardest of hardcore TG16 fans, either. You'll have to weigh your own situation.
Thanks for sharing, anyway. Whatever happens from here on out, it's an incredibly good thing for you. Enjoy it!