Sure, people may return to a website -- and even be more likely to buy from it -- because it looks beautiful. And visual attractiveness probably has some SEO benefit in the long run. If people are visually impressed by a website they're probably a bit more likely to link to it, after all.
Still, you've got to get them to look at it in the first place! And Google isn't ranking sites on their visual attractiveness. It has to judge by the actual content on the pages, which other sites link to it, social media activity, etc.
That's why I think that if you have a new site you shouldn't worry too much about making it look absolutely stunning. You should put most of your time and effort into writing the content, building some links to it and putting it in front of other webmasters and bloggers. A PPC campaign is a good idea too. Otherwise you'll feel very disheartened when you realize that your expensive visual masterpiece isn't getting any visitors at all. You can always get a top notch customization done when you've got some traffic happening.
A good illustration of the relative importance of content versus appearance comes from the Aussie blogosphere. One of the more popular local blogs is written by the mysterious Professor Bunyip. If you have a look you'll see it's just a basic Blogspot blog. It looks pretty awful, let's face it. But it gets a lot of views and comments. That's because he consistently comes up with unique and interesting content that's very well written, resulting in a lot of social media shares and voluntary one way backlinks.