I think you can be a good game designer, if you focus on that. You will need to stop playing like before and start studying the game while playing. Write down everything that you think about the game and start to answer some questions like that. Why is this game so fun? Why do i care about the plot? Is this a game that i would like to play again? If yes, why? If no, why? This is just some tips to help you. Of course this is just a small part of be a game designer.
About the idea bigger than WoW that you have in mind.
Games like WoW, Guild War 2, League of Legends, Dota 2 need a really massive budget and a lot of excellent professionals. If you wanna be a game developer, you need to start with something simple and fun. Save the big ideas for when you have money and a good team. And the most important, why you wanna be a game developer? This is a profession that you really need to love and have a solid motivation, because it's really hard to succeed, if don't have a good reason for doing this, you will have more chances to fail or give up.
That's my opinion of course. I hope that helps.
-Gleison