I really do love the NES, it's what got me into collecting. Although I really have a special place in my heart for the Sega Genesis. I would love to have a decent CIB collection for it. On the plus side since a good majority of Genesis games were plastic cases. It's much more common to find them CIB, and generally cheaper than most. Of course you have your rarities, but nothing that comes close to a Stadium Events/NWC/NCC for the NES. I mainly want to start by working toward a complete RPG collection for the Genesis CIB, as my first goal.
I think I have maybe 6 sealed video games total. Like you said, I just picked them up when I had a good opportunity.