For that matter? I'd venture to say that even for client facing employees, dress code/attire has too much emphasis placed on it in many cases.
For a long time, I knew a lot of really good, bright people in I.T. who avoided or distrusted any salesperson approaching them in a suit and tie. They knew that you could basically pull any warm body off the street, dress them up like that, and put them out there to try to sell you something. The people with real knowledge about the products or services were more likely not to be forced to go through all of that.
I know myself, I'd mainly be concerned that someone I interact with as a potential business partner looks like they have it together. Don't show up with clothes with holes and tears in them, or clothes that fit really poorly. But beyond that? Trust me.... I don't waste any time looking to see if you have designer brand shoes on, or care if your shirt buttons down vs. pulls over.
I've found that you can look fairly professional just by wearing clothing as simple as a solid black t-shirt and a pair of black jeans. (It has sort of a modern "I'm a techie." look to it, as long as what you wear is in good, clean condition and fits you properly.)