1. Even if you haven't 'mastered' all the tunes and tricks you want to, shuffle new tunes, licks and techniques into your practice routine to keep it fresh - you might pick up something that will help you break down some of the barriers in your regular routine.Keep it fresh! If you play mostly Blues, work on a Polka (seriously). Or a Waltz. Try some Jellyroll Morton. Learn a counterpoint piece. If you haven't developed a great train piece, work on that.
One of the commonest mistakes I see among harmonica players is not learning complete songs. Learn to play melodies. Learn to play Rhythm, Bass-lines, Comp with the band.
There's NO REASON you can't do everything a guitar player does, or a horn player.
It's important to keep variety in your practice to keep your playing diverse and interesting, to keep you engaged and most important, to keep you challenged. While it's very important for you to find your own voice, your own style and approach, it's just as important to be sure that approach is well-founded in the fundamentals.