Absolutely not. First, it's totally random. Second, skins are not gain by achieving something in game (like an achievement or extra display of your skill).
Hmm.. is it? I thought beating people and crushing their souls is the main reason. Dunno m8, I play to win.
Yes, they do look great - I'm actually quite impressed with the recent additions. But considering that you can't see them during 90% of your activity.. it's not that awesome. And again, they are gain through random means or through sheer force of a wallet, so you can't show of them as "hey, I got X skin so be careful cause I did Y and Z which proves my skill".
Pokemon complex - yeah I agree, some people need to collect everything. Then again basing your game model on people's OCD/Autism is kinda meh :P.