If you're going after the highbrow, trendy types with disposable income... Then yes, I think it would make all the difference. Furniture, clothing... Stuff like that. iPods and cell phones?.. Stuff that people know is going to be the same everywhere... Then no. Not so much. But how something looks is subjective. I tend to be a visual person, so I'm not really impressed with the cookie cutter type sites, when it comes to buying anything stylized. To me it says the people have no creativity, which obviously reflects on their products... Assuming they're the ones developing them. I also get annoyed by sites that are too busy, or it's like figuring out a puzzle trying to find stuff.
I DO believe it depends upon the market and target audience. Visuals have such a huge impact on our perception - conscious and unconscious. Marketers have known this for years. So if you're going to go for minimalist - make sure you do so with a plan.
My two cents: nowhere nearly as important as most site owners/marketers make it seem. Form should always follow function, and I've seen sites developed where the function is so badly forced to fit the form that customers run away in frustration. Yeah it's the coolest looking site ever, but I can't use it.
The only real test of whether or not your design is killing you is exactly that: A/B or multivariate testing of different designs. You may be surprised and find there's not a lot of difference, and that the differences you do find are a result of just moving elements around or changing some of their sizes, not colors and pretty graphics.
Services, I'm not sure. But I'm in the school of thought that... you either care about your business and how people perceive you in life, or you don't. If you have a site that looks like a 10 YO did it, then that tells me you don't care. And if you don't care about that, then you probably don't care about other stuff as well... Like my job. It's kind of like going into an auto garage and seeing spilled oil and crap everywhere. Or seeing a dentist with bad teeth.
I recently was looking for a machinist. Two guys I tried that had less than stellar sites turned out to be total screw-ups. One that had a nice site turned out to be professional (albeit expensive) and gave me a prompt quote. Coincidence? Maybe, maybe not.
Heh . . that actually makes my point. Design is more subjective than anyone would ever think, you see "ugly" in the Wal-Mart branding/website, I see "a web 2.0 site that looks like every other web 2.0 site" (and in doing so, is buying in to the customer expectations and familiarity ideas of usability.) :-)
(and in doing so, is buying in to the customer expectations and familiarity ideas of usability.) :-)
although personally I don't find their site particularly useable. but that's just me.
So yes, I would agree that your site's look / UI should match your customer's expectations. If Nordstrom had the same design as walmart, people would balk at the prices that Nordstrom charges (even more than they already do).