1) Condition - Like everything else collectable it is important. In recent years there have been companies grading and slabbing packs for that reason. (I have never owned a graded pack)

2) Scarcity - Some packs are so scarce that the wrappers alone can bring $1,000- $2,000 or more

3) Series Number - Pre 1974 cards were issued in series of 132 cards and only cards that were in that series were available in those packs. Obviously a pack from a Mantle or Ryan Rookie series would be a huge premium over other packs.

4) Trust - Resealing has become a major problem in the hobby for many years now. It is just too darn simple to open a pack and reseal it if there are no superstar cards inside. An expert can usually tell and this is another reason slabbing entered the world of unopened packs.

5) The most important factor in value of a pack as with any collectable is demand. If you find someone looking for a 1955 Topps 5 cent wax poack to fill a hole in thier collection, you may be able to sell it for many times its book value much like a chip.

Let me know if you want values on specific packs and I can come up with an estimate.

Take care and happy collecting,
Doug