MOST MODELS LOOK ALL THE BETTER for the addition of some weathering and subtle dirtying.
SMN report: Not too much weathering mind, as it's all to easy to overdo it. Here Geoff Coughlin provides a general look at techniques which can add a used look, without going over the top.
It's worth inspecting the 1:48 scale Tamiya Bf109 (below) from the 'Decoration Series' to see the unique red-and-white markings of the Swiss Air Force. Good as the model is, a touch of weathering using the methods described by Geoff would improve it no end.
