I think you already mentioned what's missing, and what could take it to the next level...and that's the drums. I know you were just spontaneously improv-ing, but you can just as easily improv with a drum loop, prolly even more so as certain parts could carry further with that backing rythym. I guess really it's not just as easily if you don't have a drum machine or whatever though. But yeah, I think to get a form of drums to practice and improv with would greatly improve anyone's creativity and ability to put parts cohesively together. I've used the drum tracks on my PS2 Music Generator out of necessity. But hey, they worked.