When I first upgraded to my Specialized Ariel, I was hesitant to add anything personal beyond the standard black rack and black trunk bag. Shortly after that, I added white and red blinky lights for safety and legality, a stem-mounted cell phone holder, and a mirror on the left handlebar. I eventually added a few reflective stickers, a front basket, and a right hand mirror (because I needed to see over both left AND right on that last big curve before entering the campus).
I then lamented to Scott that my bike looked too silly and it wouldn't be taken seriously. Scott said that my bike simply looked like a useful commuter bike and there was nothing to worry about. I continued to mull and finally asked myself who I was trying to impress. The guys at the bike shop don't hassle me about what I've done to my bike; in fact, Scott thinks that the personalization (and the fact that I don't look like the typical bike racer type) is part of why the guys remember who I am even when I don't have the bike in tow. The other commuters are pretty friendly and we nod and smile at each other as we pass on the trail. Nobody in the BikeMeDC meetup group has ever said anything derogatory. I've even gotten a few compliments on my bike (and apparel) during group ride events such as the Backroads Century and the Great Pumpkin Ride.
I say that I'm not happy unless I'm fretting about something but personalizing my bike is definitely NOT something I should worry about. So I'll keep adding bits and bobs and trade out pieces of equipment (black trunk bag for colorful Basil pannier, for example) as I see fit. If, to paraphrase the song, they see me rolling and they be hating, I don't need 'em.