My kid loves these and has them all. I am still surprised it is hard for me to choose which character / colors will be most popular. For example from Series 1, I definitely thought the reds were the coolest, but yellows were the clear winner in resale value (though reds are catching up fast). Series 2, I like the Fang Gang... all those teeth... but the slow, frozen blues are the hottest seller. Series 3, I like the tans, especially Scorpi, but current word on the street says that purples will become hardest to find. I'm guessing it has more to do with childrens' attraction to favorite colors than the characters themselves. Given a choice between a brown, blue, or orange mixel, kids choose blue (a favorite color for lots of people). Maybe it's as simple as that.
Anyone parting out Mixels yet? ... just kidding... but I was wondering... could someday the Mixel / Nixel packs become more valuable than the others? Could they be parted out? For those that don't know... each color set of three has one character that comes with one Nixel inside (Nixels are little black enemies of the Mixels). If you've seen the cartoon clips, or played the tablet app, you'll know that Nixels get together in large groups to fight the Mixels. It's possible there's some buyers out there who want to create an "army" of Nixels. I believe the current characters that have Nixels in the pack are: Krader, Teslo, Vulk, Balk, Chomly, Slumbo, Glurt, Hoogi, and Magnifo (correct me if I'm wrong... I just asked my 6 year old, and he listed them off in about 5 seconds.... he seemed quite sure of himself).
On the same note, I think Lego is missing an opportunity to print more money, by not offering black Nixel-only packs. Just like those kids who don't care about Luke and Han (but want to collect ALL of the Sith and Vaders), I'm sure there are Nixel "dark side" fans. They could also offer a variety of "boss" Nixels, like those shown on the other media.