I always bring lightweight rain pants with me. I almost never use them while hiking, but on cold, windy nights they really help, even if it isn’t raining. Weather can range from warm sunny days to hail, sleet and snow (yes, even in the middle of the summer), and temperatures can drop below freezing even when the weather is great so I like having the extra protection.
As far as water treatment goes, have you tried Aqua Mira? I hate the taste of most treatments, but Aqua Mira doesn’t bother me at all. Worth a try if you haven’t already tried it.
As for clothes, I don’t bring extras except for an extra pair of socks. For long pants, I just use my long underwear. I usually bring a silkweight or lightweight pair (lighter than regular pants) and a heavier Powerstretch or expedition weight pair for warmth at night. Also, I didn’t notice a jacket other than your Precip. Unless you are going to hop directly into your bag after you stop hiking, I would plan on bringing a light fleece or down jacket that you can layer under your fleece.
Kanga