With regards to the ranking system, I'm not really sure how it works, but i find it really stimulating (and motivating). Of course, for a restless person like me, it's my way of keeping myself stay focus enough... Like a long term goal that is fun to work on.
About competions, truth be told, i find it a very good venue. For novice like me with scattered thoughts, the competition theme works well as a kind of writing prompt... Like a little workshop room where i can try find my way (style and form wise) and see if i can do this and that. The throphy for me, if I happen to win it, is just incidental (and a welcome delight, not to feed my ego but like an encouragement for me to continue to try)
Also, in competition thread, reading entries made by others give me a whole lot of wider pespective when it comes to relating and appreciating other people's work, rather than if i just read a poem randomly posted. Maybe because i know the theme and it makes me understand their works better even if it's vaguely written with lots of metaphors and difficult words.