I think of it more like a "blank canvas". Its design looks great just the way it is, and yet it still looks good with many different modifications as well.
Strategically placed stripes, emblems, decals, vents, louvers, paint jobs, etc. can sometimes add, or deminish the overall "look" of the car in the eyes of the beholder.
Personally, I think the key word is "restraint", but that's just me. There are many visual modifications that I enjoy on other forum member's cars, but I feel if I included them on my car it would simply be "too much" (in combination with what I've already done).
What is really important, is to please yourself. If you like it, that's all that matters. The tradition of personalizing one's car has probably been around ever since the first time a "second" car rolled off an automakers assembly line.