I had this long post questioning several aspects my recent pack-lightening revelations, but they sounded dumb, so I scrapped everything but this one question:
I always bring a longsleeve baselayer top and a pair of running sorts in my pack, so is there ever a need to bring a 2nd set of hiking pants or t-shirt on a 3 season trip under a week in length?

I feel like I could just wear the above mentioned shorts and top, and wash the pants and shirt if they need it (mud or food spills), but the long-held 'just-in-case' mentality is hard to leave behind.

At what point does everyone else start adding in more 'clean clothes'?

"At what point does everyone else start adding in more 'clean clothes'?"

I was doing a 25-day trek in Nepal, so I had one synthetic t-shirt plus two spares. The spares never got used. Years later, I was doing a 20-day trek in Nepal, so I had one synthetic t-shirt plus one spare. The first t-shirt had to be rinsed, so the spare got used while the first one was drying. Unfortunately, the first one was frozen for three days which slowed drying.

--B.G.--

for a week long trip no extras, save a pair of socks- this are used to sleep in; if it's warm I often wash clothes mid-week

I typically wear shorts and carry a light pair of tights for wearing around camp in the evening/morning- if I need to wash my shorts I can slip into these

extra (unneeded) clothing was the first and easiest way to lighten the load- I even now have my wife convinced (that took a couple of years :))