Is it worth it?

Is it worth it to buy tins and promo boxes as they come out, then save them unopened?

I ask this because I always see old tins from like 4 years ago pop up on Ebay for pretty high prices, and I also know that tins from the ex series go for quite a bit. So, would it be worth it to buy the new tins and just keep them sealed for who knows how long?