Just because you know some music theory doesn't mean you have to use it for everything you do. You can still sit down and play creatively without thinking about what you are doing. But armed with a bit of theory knowledge, you can now more easily expand upon that cool riff and turn it into an entire song. I often use this approach in my own song writing. I will sit down and mindlessly start cranking out riffs and lead lines until I find something that sounds cool. Then I will take the time to analyze what is going on musically: the key, the chords, the scales, etc. Once I have a general idea of what is going on, I can then use that knowledge to quickly expand upon the idea and come up with a vast quantity of usable material in half the time.
Another huge advantage to learning theory that should be obvious to all of you lead guitarists out there, is knowing how to intelligently construct a guitar solo. Sure, you can learn a few scale patterns and try to move them around the neck until you think you found what key the song is in, but that is very time consuming and often leads to dull and boring guitar solos. Not to mention you'd be completely lost and unprepared if the song changes key or uses a secondary chord function. Knowing theory allows you to thoroughly analyze what is going on with the chord progression you are soloing over and make deliberate and intelligent choices that will completely dictate the emotion of the song during your solo.
But what if you are just learning guitar to have fun playing cover songs? Music theory still provides a great advantage in this situation as well. Ask any seasoned guitar player that knows a little theory and they'll all tell you the same thing; having the ability to analyze a song musically will enable you to learn songs quicker, and greatly increase the efficiency of memorizing the song. It also allows you to have a bit of creative freedom with your interpretation of the songs you choose to play.
So if you still think music theory hinders creativity, I challenge you to research some of your favorite guitar players and try to find out their take on learning music theory. I can guarantee that the vast majority of professional guitarists know at least some theory and this is how they are able to develop their unique sounds and playing styles.