yet I hardly get new challenges to overcome
This is really an impossible problem to have on guitar. Here are a few tips:
1. Can you read music? If not, learn. Buy "Modern Method for Guitar, Vol 1" and dive in. It will open up whole new worlds.
2. Can you play jazz, country, blues, classical or other styles that might be related to what you already like? Start delving into other genres of music and you'll have a million new challenges. Once you learn to read music, a whole bunch of music not written for
guitar will be available
3. Learn some new techniques. How is your chickin pickin? Can you play with a slide? How is your legato? Are you bends precise? Do you have total control over your vibrato? Speaking of which, how is your vibrato? Musical? Non-existent?
4. Learn some new chords and voicings - Ted Greene's "Chord Chemistry" is a gold mine.
5. Buy Victor Wooten's "The Music Lesson" and read it through. If that doesn't light a fire under you, I don't know what will.
Good luck. Everyone gets in slumps now and then, but fortunately there are a million ways out. You just have to find the way that works for you.