Wow, folks... thanks so much for all your input. I also really appreciate the welcome messages.
Taking the advice of edl and others, I did an analysis of my output from the P&S: ("for i in */img_????.jpg */????.jpg; do exif -tFocalLength -m $i; done | sort -n | uniq -c" plus some spreadsheet action). This reveals that fully 68% of my P&S shots are at the wide end (35mm in 35mm-equiv), 8% are one or two stops narrower (48mm), 7% are at the long end (140mm), and all the other zoom stops are around 1 or 2%.
I believe this confirms my intuition that I want a wider wide and a longer long; I clearly bump up against the wide all the time, and the longest long is the 3rd-most-common setting. I also know that I pass up many shots because I can't go long enough.
I think that it's OK that the candidate lens is a little heavier; with the greater reach, I can go on my April trip and see what focal lengths I end up using. If I don't use the full reach, I can reevaluate then.
Also, the story changes slightly, as I found a couple of 1970s-era fast screw-mount primes in my closet (as detailed in
another thread), a Vivitar 28mm f/2.8 and a Takumar 50mm f/1.4; the latter is apparently quite a find.
I might take one of them along: I was thinking a little more about the one-lens-only requirement, and I think I missed some nuance earlier. It is true that
during the day I absolutely want only one lens, as there's no time for fooling around with lenses when most people on the trip aren't photographers and there's lots of ground to cover. However,
in camp this requirement is relaxed: I can go in the tent and change lenses; no one's trying to get anywhere; etc. Pleasantly, during the day is when there's the most light, so it's OK if that lens is slower.
I think it smells like this plan is a good fit.
Thanks again,
Reid