Business: Graphics affecting conversion?

I'm working with a local company here in Sacramento, cleaning up their mainstream website and setting it up to actually convert. Basically my question is how much of an effect does a graphical interface have on conversion, versus a purely text based interface?

Speaking from personal experience, I think I'd rather buy from some place that looks like they sunk some money into a nice site design instead of just having thrown up some links to products. I think text-only sites look a little amateur.

But that's just my personal opinion. The bottom line is conversion. Do either of these scenarios actually play a part?