I don't think this is a bad idea at all as an option. I've hidden the voting booth lately because of the amount of space it takes up among the nodelets. I wouldn't mind being able to turn it on or off based on my participation.

 * Not exactly the mentioned solution but users can go to Nodelet Settings and set the voting booth to appear only on front pages (or other than front pages) if they still want to easily see the voting booth without it appearing on every page.