I think what you are describing Mark is essentially correct, and it is also a common technique used by Jazz guitarists as well.
As for patterns, melody etc...as it pertains to fingerpicking, if we're talking along the lines of Travis style, the fundamental is getting the "boom-chick-boom-chick" going with a steady alternating thumb, and developing simple patterns for the other fingers to pick out over the chords. Once you've mastered that you're ready to explore improvisation, while keeping the thumb going.
(Without any intent to kiss ass) the best advice and instruction that I ever got as far as how to open up the improvisational elements in fingerpicking came from Mr. Fielding during one of our early lessons. That advice was to take any standard major chord (ie: C, G, A, F, E, etc.) and while maintaining an alternating thumb bass, try and play a full scale ascending and descending, around the thumb. Once you've got it down over one key, then switch to another. You will be amazing at what this exercise will open up for you. Not only will it get the fingers stretching, it will help your independence, and open you up to more exploring. And if you're a ragtime player, it will make you a better one!