I think the important question is how a windshirt is used. I'm surprised how many don't really grasp the concept and reach for heavier and less versatile options rather than a coordinated layering system.
I think of a windshirt and other layers as an insulated jacket that has been disassembled, with the windshirt being the outer shell of a system that will protect me from convection heat loss, harsh sunlight or insects, and light precipitation.
My favorite options for layering include:
*A simple polyester base layer, with long sleeve being the usual form
*A light mid-layer like R1, Power Stretch or 100w fleece. I find a vest is great for summer use and a hoodie for colder weather
*An insulated vest like the Patagonia Micro Puff or REI Revelcloud
With these options I can layer up as needed and this is where the extra room in the Houdini design works-- you can add a light layer and still have a comfortable and breathable system.
I would normally take the windshirt off when adding a rain shell, but if I was in camp and things were too cold, I would add any layer that helps. Likewise for sleep.
For on trail use, I might start out from the trailhead with a windshirt on if it is chilly and usually end end up unzipping it or taking it off as I heat up on the switchbacks. It is compact enough to stow in a lid pocket or bungies. It is there to add on a rest stop or as the terrain and my exertion change, or as the weather dictates. I might put the windshirt back on when I come to an exposed level traverse across a slide area or going down hill.
A major challenge of Pacific NW hiking is the steep terrain coupled with high humidity and light precip. You really do make a decision whether the rain or your perspiration is going to make you wetter (or colder). A windshirt often makes the decision in the favor of the hiker's comfort.
If you have any doubt about the advantages of wind protection, put your windshirt on and take off in your car on a cool day and stick your arm out the window at 60mph-- it is amazing what a light windproof layer can do.
Finally, you don't have to buy a $125 4oz garment to get the advantages of a windshirt. There are many on the "windbreaker" side that are in the 10oz range. Many are designed for runners and track warm-up jackets and can be found in the big box stores or discounters like Ross or Marshalls for much less. I see them in thrift stores all the time for $6-$10. We're all about weigh here, but that one item won't change your base weight much and will introduce you to the windshirt layering system without breaking the bank.