Actually I find Mario is considered "cooler" with adults than most gaming IP, even hipsters and all that.
Wearing a Mario t-shirt is cool considering you'd get laughed at for wearing a "Kratos" t-shirt or something as an adult anyway.
Mario halloween costumes are always popular with the college crowd too, I find almost at any big Halloween party you'll find even girls dressed as Mario/Luigi:
Just this week too, Dancing with the Stars did a big Mario themed dance number too:
https://www.youtube.com/watch?v=lK2lDKnjn6M
Mario is still very well known and well liked by adults. Nintendo's problem though I think is getting these people to buy expensive propietary hardware to play just Mario. It is a tough sell these days. They like Mario but they already get their gaming fix from their iPhone (especially women).
