The only time I got a free skin is when I pointed out that I had this summoner name way before they created the ranked tiers and now people flame me for my name cuz I'm actually Bronze-skill.
I asked for a free name-change, I figured they would hook me up since I was such a high-roller customer (I had spent like $3.5k at that time). They said no.
I pointed out that if I had a grossly inappropriate name like "Lick My Ballsak Plz" they would have given me a free name-change, and that seemed a bit backwards.
They didn't respond.
Next time I logged into League I got a free mystery skin from Riot. Koi Nami. Woot.