Subtle weathering really adds that “extra pop” to a scale model. Highlighting panel lines, grease streaks, all the little things that show up on a full scale aircraft can be reproduced on a model with various techniques. Just be careful not to over do it and know your subject, for example, the Blue Angels jets are washed and waxed daily before every performance so many highly maintained aircraft won’t show much weathering as a tactical aircraft on an aircraft carrier subjected to salt spray daily.
Here’s a video that shows some great weathering techniques on a foam jet that can be applied to a variety of models. Enjoy!