While in my case (Candy Japan) I'm not sure if the possible improvement in conversions would justify spending money on the design, I wonder if the side benefit of getting listed in CSS galleries would make it worth it.
From our standpoint, it helps out with getting some solid back links for SEO purposes in the beginning and also helps from a referral standpoint. We also just like seeing and spreading great design. We're kind of passionate about that. Some designers will send the link to their non-designer friends because they don't feel like doing it pro-bono for their friend and the money their friend can pay just isn't worth it to create something from scratch.
However, if you have a product or service whose direct customer is designers, then you might be able to get some conversions from the CSS galleries. Your's could be this case.