I think word of mouth is your best advertising.
Something Bob mentioned to me when he introduced me to some cute girls from Trade The News (one of your advertisers). He realized that we old timers don't see the ads. You might want to change that during an off hour (say 9-10 pm) to help your advertisers reach out to folks- especially if all your freebie accounts sign on <g>. (Bet a few folks won't like me now for bringing that up, lol)
As far as getting the uninformed freebies to switch over, might look at a small increased Happy Hour- say 5-9 on Fridays. Give them a chance to really explore the product, without them getting a chance to abuse it.