I get the impression that you're already on the right track.
One somewhat simplified way to handle it could be like this. EQ the acoustic so that it doesn't take up too much sonic space, so that it becomes mostly a rhythm instrument. By that I don't mean rhythm as in "not solo" but as in
rhythm. The strumming is what you want to hear, not so much the tonal aspects of the instrument. That puts the acoustic clearly in the rhythm section, where an acoustic can add lots of texture.
One electric plays between the nut and fifth or seventh fret approximately, bridge pickup, doing the Luther Perkins/Don Rich kind of stuff (or flashier stuff if desired, just stay out of the vocals space).
The other electric plays from fith fret and up, middle or neck position, and plays little inversions, double stops, chord fragments, faux steel bends and such. This is where you add atmosphere. This is where you get under their skins.
I love to be in this role. Play so little and add so much. When you can play softly and still be heard, you know you've found your spot. After a while you may even start feeling very cool, just by playing very little.
Oh, and a good amp at the verge of breakup makes it even more fun.
For variation, add some tremolo to either of the guitars and let it play even less. Just let a low down root note or a three string chord further up ring. Don't use tremolo on both guitars simultanously though!