I've passed over sealed games for open games. A local game store prices them the same. The price is based on title, doesn't matter if it is loose, complete, or sealed. But I figure, someone else will get more enjoyment out of a sealed game than I would who will just open it up.
Now, I do have a few sealed games. They are doubles and were found insanely cheap. They are some Game Gear games I found for $1 a piece. I plan on keeping these sealed. After so many decades, I kind of forgot what it was like to hold a Game Gear box. It's also the only system I have that has the horrible cardboard boxes. So, I plan to keep a few as a personal historical reference of... "this is what Game Gear games looked like". The sealed aspect just means I'm not opening them, bending the cardboard, and ruining the box. They seem to stay dent free easier when sealed. I know that thin plastic can't protect it, but somehow it seems to.
I don't see a big difference between sealed and unsealed Genesis games.