dude.. ur site is gud.. informative.. 
but putting word out and advertising wuldn't hurt...
i think what u can do is.. set up a fix budget and instead of giving gift cards randomly.. put up a trivia question, or maybe a photoshoot challange.. or just start a discussion... and from within the participants.. choose a winner..

gudluck with ur site.. have already been following your posts.. so keep up the gud work..