After all this theoretical stuff (it's important - no doubt) i'd like to remind you of the second, and IMO more important aproach to soloing (and music in general). Knowing all this theory is fine and it will help you out when you are stuck. I´d suggest you use it as some sort of security system when your ear and heart can't help you anymore.

What i´m talking about is getting comfortable in improvising by ear without knowing what key the song is in. This can be learned by training your ear. To me, this is - apart from learning to technically master the instrument - the most important aspect of music. Beeing able to instantly interact with a piece or other musicians - no communication, no thinking - just emotion.

I personally learned it by working with my ex-teacher in studio on a very huge zappa-esque production that we´ve been recording for the past 4 years (and still no end in sight). I remember the first time i entered his studio. I sat there with my guitar, slightly nervous, and listened to one of his pieces which i´ve never heard before. Then he said "now play". I had no idea what to do. I helplessly stumbled across the fretboard desperately looking for the right notes. That was the hard way learning to trust your ear since his music is FAR from beeing simple. But now i´m thankfull for that.
Each time i went into his studio i improved. I have improved my ear and my feel to a point where i can instantly create lines over almost any given chord progression without beeing told about the chords in advance. Of course every now and then you will throw in a wrong note - especially when it comes to wierd chord-structures but thats just natural.

Having learned this lesson, music is way more fun since it comes more natural. i sit there listening to a tune on the radio or any given CD and i can play along without having to think about "now what progression could this be and what mode could i use". I remember a time when i was unable to put a tune that i had in my head to the guitar. Now i can.

Listen to as many different styles of music as possible. Try to play along with any given song. Listen to what the other musicians do. Don't think the guitar is the most important instrument in a band - its just one aspect - there are also times when playing the right thing means to play nothing - after all music is the space between the notes. Record yourself and monitor your progress. Trust me - this is the most important waste of time imaginable! Its more fun than practicing your scales up and down the neck. I´m not saying you should ditch all theory - but don't let it become a cage for your musical mind. You want to express yourself musically. That requires a certain level of maturity. Lerning to be yourself and express yourself honestly is a way of personal growth. Try to see the whole picture. Technique and theory are just parts of the puzzle - not the whole thing.