Music is an expression of YOUR thoughts, emotions & ideas. Think of playing a guitar solo like making a speech, because its really similar. You're asking for everyone's attention, make sure you have something to say. If you're just regurgitating a bunch of riffs you've learned, its probably not going to sound too original or inspirational. It's like watching someone stand up and make a speech, and just string together a whole bunch of important sounding words, great quotes with no context, and believing that it was a great speech because it was grammatically correct.
So try this. Listen to what you want to solo with without even having the guitar in your hands. Forget all you know about scales and chord structure; just close your eyes and try to hear the solo in your head. Hum it if that helps. When you feel a spark of an idea, that's the time to pickup the guitar, and start putting the notes you heard in your head together.
Remember, all the riffs, theory etc.. are just tools for you to use as you express your creativity. I believe in what The Edge said, in that the really good ideas come from your sub-concious. Try to tap into your instinct more than "thinking" your way through a solo.. and don't be afraid to take chances.
If it makes you feel any better at all, I once read an interview with David Lee Roth, and he was talking about Eddie Van Halen recording guitar solos. He said Eddie would lay down about 5 different solos for a song, and say "what about this one, or this one?". Roth said he thought they all really just sounded the same. I think everyone has to break out of the rut at some point or another. Even the greats don't record a hit or even a memorable solo every single time. Maybe post something in the listening post and we'll all rip it to shreds?! Just kidding! But really, I'd like to hear what you're recording.