honestly I don't think they add much value. There lots of none interactive porn already out there.
I have payed for snapchat, honestly if it's not 'for life' I don't do it. Most snapchat feeds are are i'm going on cam, I am on cam, I just finished camming. I don't know if I still have interest in picking up any more. It's cool having the message a little while. Half the time for life translates into till I boot the monthlies off.