It too took me much too long to start practicing with a metronome when I returned to guitar after my decades long break. Beyond the great help building scale speed I was pleasantly surprised with the improvement in chord changes/progressions that it brought about. For me, it seemed to build a more natural, 'don't think about it' chord change ability.

When a junior-high kid practicing guitar I never used a metronome even though we had a beautiful antique one from my grandparents. I would have done much better back then if I had used it. Wish I had it now...