After about a year, I was fed up. I’ve created a theme for Vanilla and a theme for Rocket that, design-wise, are a huge improvement over the default. Looking at analytics, they seem to be doing a better job of converting customers through the checkout process as well.
You can take a look at these custom FastSpring Classic themes here for $29. It’s a super hand-run operation though, so prices are negotiable. If you need a theme built for your product, get in touch as well.
Sadly FastSpring Classic is being phased out in favour of FastSpring Contextual Commerce, which has much more limited customization options. That’s what I haven’t spent time on making the process of getting a theme easier and more automatic, and why I’ll do everything by hand for a while.