I believe that you have some heroes/runes unlocked as well as have some riot points available to spend (you can use these to buy skins and boosts, though you could use them to unlock heroes as well but its best to just spend IP instead since IP is attainable through playing while RP is only available through purchasing...)
Also I think that you have a bonus skin in the CE as well
I played the game and decided I really wanted some more heroes to play. It was well worth the $30 in my opinion. Very fun and when you get sick of one character, you can play another. Not to mention a free $10 value of Riot points.
The Prince approves http://img9.imageshack.us/img9/7130/img0947k.jpg
Depends on how much you play League of Legends in my opinion. If you're casual (which I doubt anyone is), then don't get it. If you're addicted, think about getting it if you have the money. It's well worth it considering you get most of the champions at a low price compared to if you played and bought every champion or used Riot Points to buy each individual champion.
I'd say it's worth it... You'd get really tired of the same 10 heroes or so in the rotation... Buying a bundle gives you 20 more Champions to choose from.
I bought it myself. The amount of time you save to actually try the new heroes out is definitely worth it. Of course, it's up to you if you actually want to pay for the game (which are you already did).