Spring/summer casual for the 40 year old is easy. In your case, the move from cargo shorts to lightweight chinos in light brown, white, and maybe other pastels if you want, will make a big difference. Polos are fine but be picky. Solids that contrast with whatever you wear as pants are always good. Short-sleeve button down shirts in madras, poplin, any weight of cotton or linen that you like, are good. Popovers. For shoes you might look at suede plain toe bluchers ("bucks") and loafers of the Alden leisure handsewn variety. They are a bit more neutral and versatile compared to boat shoes. A lot of my summer pants are by Hickey Freeman. They do chinos well in my experience. Otherwise everyone sells this stuff. Stay out of malls. Go into better independent men's stores when you travel--you are a pilot--and see what they have. And buy what you like. Don't be afraid to pay for quality. $100-$150 is not too much for a quality summer shirt that you love wearing and that looks good on you. Economize by purchasing fewer things. A small rotation of high-quality stuff you love is the way to go, especially with summer wear which can pretty decadent in terms of wearing pleasure. SF is a good place to learn about stores worth visiting when in you are different cities. Ask or use the search function.