I like the hats but it seems you've stopped making new ones. If they aren't selling well enough to warrant adding more you should drop the price, maybe $5 at the most for a "cool" hat and $1 or 2$ for others. You should add some new ones to pair with the subscription packages as well and occasionally vary up the hats attached to them currently with some of the hats that aren't available for purchase any longer.
Pretty much no or little correlation between lower price and more sales from what we've seen. I think the hurdle to paying at all is the biggest part of it, and thereafter the coolness of the hat itself matters most.
"The psychological trials of dwellers in the last times will be equal to the physical trials of the martyrs. In order to face these trials we must be living in a different world."
Character customization doesn't have to be free to get people interested you already know many players enjoy these aspects of the game in the form of variable materials or sketches so of course there is room to expand on that for the player character too. As mentioned earlier, hairstyles, facial hair, tattoos and paint would be nice additions and I'm sure there's much more than just those when you start getting in to object/equipment customization.