Before I'd started this 2 year surf sabbatical, ya man, I was going through plateaus of playing all the time. I knew what my ears liked to hear, and I knew what guitars and amps/amp settings got me what I wanted to hear, but alas, therein layed one of the problems - nothing changes till it changes. I found unplugging, or going "clean" channel with some different tones changed up my style. Swapping out guitars too. Furthermore, as to not add insult to injury, I sucked at 7 string playing at first (and likely will suck at all playing when I return, eventually), so rather than play plugged in, I'd just hang with my lady on the sofa, chillin', talkin', and just going over scales and fundamental progressions, silently, but getting my fingers "acquainted" with the extra string and neck width/scale. I always favoured Lesters, but played my ESPs for speedy shit. So, I'd mix that up too - play speedy shit on my Lesters and played bluesy, smokey, slow shit on my ESPs. Different amps, sometimes an FX here or there for "inspiration", sometimes no amp at all. Just play for the sake of playing...next thing I'd know? Hey - new lick here, new progression there, new tone here, new style there.
I also have to say in my PARTICULAR case, new music (new "good" music, needed to qualify that) always inspired me too. And man, I don't know if much has changed but before I left to hit Central America, there wasn't anything that caught my ear other than the latest Deftones and AIC albums. But there wasn't anything that made me go "I gotta nail that lick!!". So, hey, listen to some different stuff, not the normal stuff.
Hope this helps, and bottom line? Everyone who plays an instrument plateaus - everyone. It's part of the game. Those who rip are those who keep picking it up despite their lack of enthusiasm; those who end up sucking and getting worse are those who don't push through. Simple.