Are old Magic: the Gathering boosters worth more sealed, or should I open them?
Logically speaking, it would never make sense for the expected value of an opened pack to be higher than the value of an unopened pack.  If that was ever the case, people would just buy unopened packs, open them, and sell them for a net profit.  Unopened packs have the potential to have a high value, and that potential reward comes with an associated increase in cost.