Varied Line Weight in Illustrator

I was experimenting with techniques for creating an organic, varied line weight in vector apps like Adobe Illustrator and came up with this approach.

Cartoony illustration is not really my thing, but I thought it might be a good choice for a poster for local Jazz Festival. To get the varied line weight, I drew each line twice -- first forwards, then immediately backwards -- loosely retracing the first line. I let Illustrator fill the resulting closed loop. No stroke was used -- only fill. I was sort of going for a style like that in the old Anna Nicole Smith tv show main titles.