I will not pretend to know if the value appreciates better if the fig is still sealed. I would assume that it would, but you never know with the ?Mystery? figs. Personally; I open & display them. I also have several duplicates still sealed for resale in several years when the value is high. I would say that there really is not much difference in the price of a complete set sealed vs. a complete set opened. If you add up the cost of the individual figs & compare them to a complete set lot; they are pretty much cost the same.
I really just wanted to tap in to say that the "feel" system is not the only way to identify the Minifigs concealed within the bag. Lego made sure that they could identify the individual figs so they incorporated a braille system to quickly identify the contents. This is commonly known as the "Bump code". If you look at each bag; there are dimples (or bumps) on the bottom seal. Each fig has a different dimple layout/pattern. If you google "Lego Minifig Bump Code", you should be able to find the codes for the series you desire. Be patient with newly released series as it takes a lil' while before some deciphers & publishes the codes.
Personally; I use the "Feel" system as this is much easier then the Bump codes. Many times the Bumps aren't profound enough to easily decode. If you are even the slightest bit familiar with Lego's Minifigure designs, you should be able to identify the parts fairly easily by they're shape. It's much easier if you have a picture sheet of the minifigs included in that particular series. This way, you can match what you feel to what you can see.
