Yeah I think it is definitely worth the effort. I agree with fctoma, you won't see an increase your rankings. However you will broaden your exposure. I see 2-3% of total traffic with 3+% conversion. That is not bad for free traffic. If someone is searching for a product that you offer and Google Products serves it in search results it will be highly relevant which should lead to sales.

I am considering expanding and using singlefeed to help with other shopping engines. Anyone have feedback on singlefeed?