Oh god... I'm just as horrible at this. I always say "This is gonna stay sealed!...", but I always cave so hard... Uhhg...
If you're even considering the option of leaving it sealed, then leave it sealed. I'll put it this way: you know the songs that are on the CD and it's possible to get quality rips of the CD for your music player. Unless they aren't worth a whole lot more left sealed, I'm not very familiar with the prices of LP merch.