Despite whatever progress you make, 20 years from now you'll still be yearning to expand and hopefully never be content and satisfied...as it should be. Even (insert your favorite guitar hero) writes stuff that doesn't really thrill them to death...sometimes even the very songs others grow to love. But try seeing it as though you already have improved.
And the best ideas are hardly ever intentional...the "muse" has to visit you and spontaneously an idea will start to flow. To help initiate this though, I suggest setting up a tape recorder and just letting go. I'd say a tape because you can just hit the button and leave it alone for up to 30 mins or so...helps you forget it's there (important) as opposed to on the computer or whatever other medium requires more frequent attention. Then you can review it and salvage what parts are worthy and then intentionally expand them. So far this has been one of the most rewarding feelings I've gained from guitar...hearing a crappy recording of myself yet going, "damn, that was pretty cool, how the hell did I do that?" But yes, those moments are somewhat rare and fleeting...thus the suggestion of recording to capture them.