Ecommerce SEO - Product Meta Descriptions

How important are product Meta Descriptions? We are an ecommerce store of roughly 2,000 products. Is it worth going through all products and updating the meta descriptions adding in keywords from our keyword research. Lots of our meta descriptions are too long or too short from our bulk product upload, but I've also read that Google re-writes most descriptions and also doesn't use the descriptions as a ranking factor. So is it worth spending the time re-writing them?