Friends have helpfully weighed in with suggestions, ranging from the Nikon 1 through the Canon S and PowerShot series. After looking at a lot of specs and reviews I decided to order a Fuji XM-1 body and a Fuji XF 18-135mm f3.5-5.6 zoom. The XM body is light at 10 ounces, partly because it has no viewfinder, but uses the same APS-C sensor as costlier and heavier Fuji models. The zoom covers the focal range I'd like to have, though it weighs a bit over a pound. Still, the combination is half the weight of my Pentax K-5 with the Pentax 16-50mm f2.8 zoom attached.
Fast forward: the XM-1 and lens arrived. I put the lens on the body, and immediately got an error message: "Lens Control Error". An email exchange with B&H suggested doing a firmware update (to version 1.20). Because the lens was released after the body, the thinking went, this might fix it. I dutifully ran the firmware update but it didn't solve the problem, so the whole lot is going back to B&H.
My wife is telling me that I have the worst luck with cameras. She may have a point. My K-5 was defective when it first arrived, so I waited around while Pentax looked at the body and decided to send me a different body along with the adjusted 16-50mm. I'm not sure the 16-50mm is at full performance anymore (see here). Come to think of it, the only digital camera I've owned that never had a problem was the one she gave me for Christmas in 2003: the Canon Rebel. Maybe I should let her choose my next camera...or maybe I should return to the Canon fold. I grow weary of the chase.
In fact, I wearied enough to order a Canon: the PowerShot G1 X Mark II. It will arrive in a couple of days. Stay tuned.