Guitar Nerds Anonymous

Any ideas for how I can get a bit of that early enthusiasm back? Could it be I need to make a conscious effort to play with other musicians and if so what's the best way to do that? I used to do some jams with another guitarist but we were on completely different wavelengths about the styles we were into so that failed pretty quickly and sort of put me off playing with other guitarists. Maybe someone on a different instrument would be better?

Don't force it. You can't switch creativity on and off like a button. You need inspiration, it usually helps to find some new music you are really impressed with, or rediscover some old music you used to like, go see some live bands, check YouTube vids. Think about any songs you've always wanted to do a cover of...
Don't rely on others, play with a bassist/drummer/piano/whatever by all means but don't make them responsible for your output.