Ah, money, with time the limiting factor in most of our lives.
As for my thoughts, here I go:
For a 2 to 3 day trip, I'd carry just two pairs of socks - one I wear on the trail and the other I wear to sleep. Never the two shall mix except on the last day, when you can walk out in your sleep socks.
I would agree that the carrying shorts/rain pants and regular pants is overkill.
In either case, I'd carry the DriDucks.
But I would wear either the shorts or the long pants, leaving the other at home. And I could see swapping both out for convertible pants which have zip off leggings.
The long sleeve shirt works great for sun protection. Do you like hiking in long sleeves? Do you find you need a Columbia Windshirt for warmth? If you really love the Windshirt - and many do - can you wear it with a short sleeved shirt?
These questions are difficult, because where you are in the Central Oregon Cascades can make a fairly large difference - as you approach The Sisters weather patterns change and there is generally more moisture. Also, the time of year can play a big difference.
I prefer a good down jacket for evenings, which can be cool. If I need more coverage while hiking, I generally just wear my rain shell.
A very inexpensive substitute for your 4 mm thick groundsheet is the PolyCro ground cloth offered by Gossamer Gear. It is 1.5 ounches for a 40 x 96 inch sheet, costs $8 for two sheets. When you first unfold it, it has a tendency to stick together. After a few times in the field, folding it becomes a snap. And mine has lasted 60 nights thus far with a few minor repairs with tape.
You don't have any thermal underwear, if you are going in the midst of summer maybe it's not necessary for you. I find that I sleep cold, so I use them all the time. But again, that's me.
If you like your other gear, I'd just experiment to find what works. I am not a huge advocate to change out gear if ounces is the only consideration. If you sleep well on your pad, by all means, keep using it. If you like your pack, well, there are lighter versions, but packs are quite subjective in fit. And TP? Well, that's a real personal issue.
I found water not to be exactly plentiful in certain sections of the Cascades. It was hot when we passed through, and having more than two liters of capacity nice. Of course, every year is different.
Best of luck