Sometimes i will just make finger excersies or take something i've heard in a song and i use that to pratice speeding up my playing. Like this:
|-7--------7--------9------------9-------------|
|--8------8-8------8-10--------10-10--------10-|
|---7----7---7----7----9------9-----9------9---|
|----9--9-----9--9------11--11-------11--11----|
|-----10-------10---------12-----------12------|
|----------------------------------------------|
^ that lick looks familiar to me now, i have no idea what its from though.
So i'll practice that above for like 5 mintues at different speeds.
You could also listen to some of your favorite guitar solo's that involve a decent amount of speed. And figure out what finger action they are using ,ie: slides, hammer-ons, pull off's , bends, etc.
Arpeggios make for good practice as well for spicing upo a solo. It may lead you into combinations you might havent thought of before
You said you use alot of scales, one thing you could do you make the solo richer, or fancier is change the key acorrding to the song, then you could change scales easily, and you wont be so limited. Also practice your scales in various intervals (thirds, fourths, etc) in every scales degree.
Also remember to use alternate picking. I see alot of players only down picking, you can only go so fast doing that.
Once you start doing things to get your speed up, it will grow in spurts, and then maybe plateo for a little while.
I'm sure some of the big guys here will have better advice for you :)