if you prefer to keep them sealed for aesthetic or display purposes then do so, as opening any toy will decrease it's value. There are collectors here that only collect MISB/MOSC, again that's just a preference.
If you do open them keep the backing cards in a box etc and get yourself an expandable file for the instructions. Look at it this way: For the $12 that you've paid each for them, i say open them up and display/play. Do you keep DVD's that you've payed $12 for sealed and not watch them?