We believe less than 500 medal cards were produced of Mantle. Sorry, we don't list a value for this card. I would say more than anything they have allowed people to buy and sell faster. What it probably has done is created greater demand for graded cards since graded items sell faster and for higher values online than non-graded cards because you know exactly what you're getting. That's true in this industry as it is in coins and other collectible industries.
Uncirculated material is considered more pristine.
As for selling your entire collection, you won't necessarily get more for it all at once rather than selling individually. Different sets have different values and different demand from the hobby. Years ago I received a glossy picture of Babe Ruth from General Mills. I still have the envelope and picture but neither have been cared for very well. I received this picture.