My theory on hiking gear is this . . . it needs to function for you, protect you, and function for the hikes you do.
I live in CO and hike mostly in CO and the greater southwest. I pretty much never wear shorts on a hike. I will only wear them on groomed trails in the heat where I am not going to have branches slapping me in the legs or deal with mosquitoes and ticks (i.e. hiking on maintained trails in the desert, canyon country, ect). For me, long pants in various weights and tough fabrics are gonna protect me from getting cut up when I fall, clamber over rocks, or walk through brush. They also better protect from insects. I wear tall boots because I like to be able to do minor river crossings in my waterproof (gortex) boots and because the tall boots keep insects and stuff out of my socks and legs. They also protect my feet from rocky terrain. I have strong ankles and rarely hike with a heavy pack, so the ankle support isn't important to me. I personally don't like most zip-off pants since they often don't fit over a pair of boots, so you have to take the boots off and by the time your done with all that you could have just rolled them up if your worried about water. Boots with a too-stiff shank (used for heavy hiking and true packing) will cause cramping or muscle strain for some people.
I'm a huge fan of long sleeves for the same reasons . . . lightweight breathable tech shirts with long sleeves protect from bugs and sunburns and abrasions with minimal chemicals.
I always wear a hat, either a ball cap, something with a wide brim, or a beanie. I often will wear a wicking headband or wrap under my hat. Protecting from sun is a big reason for me, but may not be as important in WA.
Instead of Tevas, I preffer a closed mesh river shoe for river crossings (to avoid slicing feet up) and something with more support and protection (trail runners, sandals like keens) for hiking in hot weather.
I also find a rain jacket or water-repellent wind repellent layer important, and a fleece or wool layer.
Honestly I think it depends on who you hike with, where you hike, and how long/hard of hikes you are going on. I regularly do an 8-miler and a 10-miler with minimal water crossings in my jeans and trail running shoes. YMMV
