So, with the help of a colleague's email, I figured out which Dells I should be looking at: the E4200 and E4300. The reviews of the E4300 don't make it look that good; the E4200 gets a better press, although most of it in more general circulation magazines than in the sort of fanatic's web page I tend to trust.
The E4200 with most of the trimmings — said to have many internal components in common with the Lenovo X200 (not X200s), although a somewhat inferior casing — is a 12” laptop with decent battery life, a 1.4GHz Intel Core 2 Duo ULV SU9400. Despite the low-power chip, the Dell has a better benchmark (PCMark Vantage 3582) than the Lenovo X301 (1.4GHz Intel Core 2 Duo, PCMark Vantage is 3157) although I worry the test may have been affected by using a new SSD. The Dell apparently weighs under 3lbs even with a six-cell battery (2.2 lbs with the 4-cell; Dell is annoyingly coy about about the weight with the six-cell version.) There are fewer ports than the Lenovos, but probably enough for my needs.
Prices for new ones are outrageous — I just configured one for $2335 which is more than the better, if heavier, Lenovo. A similar E4200 is available refurbed for just over $1300 with external DVD, which is notably less than the Lenovos.
This is probably the closest thing to a modernized Inspiron 300m. Is that what I want? The refurbs are mostly black, but there's also a red one.