As far ebay prices for instance, why is something supposedly in "mint" condition let's say, $50, but the same card BGS 9.5/10 is $250. I know it's nice to have, and solidifies the fact that the card is actually mint, but does it really increase value this much? Just something I was thinking about.

depends on the card...like the david price sterling rc auto's sell 55 raw and up to 150 easy 9.5, and the 10's go for 300 plus

If the card is from a condition sensitive set a 9.5 or even a 9 can really add value.