I have been messing around with chormatic runs,( dabbling ) off and on, and I always come back to the same conclusion. Too many notes in a song,( especially notes form another key ) tend to dilute the interest, and strenght of a peice. I myself use all 7 notes of a key for effect, and trying to work in chromatic notes just does not sound right to me. I mean every once and a while I will hit on something, but no big deal. Certainly not worth the extra effort. Not to mention the adjustments the other band members may have to make to blend. I recommend sticking within the root key for the most part. This whole changing key subject is over for me. Besides after 22 years of playing Im still finding new cool sounds in just one key, no problem. Extra notes not needed. You know sometimes I wonder if some people use that key changing excuse to cover for laps in technique, and the constant practice needed to stay in good form.
But thats just me.