One thing that kills it for some reason is named.  We are running a
  dedicated name server machine, and all it is running is named.
  Sometimes there is something like 40MB of swap claimed, and the
  aparent sum total of the processes is something like 15MB.  The
  machine has 16MB of RAM.

If you are taking lots of bogus requests of the form other.domain.your.domain
you will negative-cache the intermediate failures. this can mean 2-3x 
overhead for each lookup you serve.

If you have 4.9.3 in default config, you have STATS enabled and get a lot
of overhead per data entry. Its useful but has memory costs.

A popular and well used DNS server is going to be big. we have 40Mb servers
with almost no negative cache crap and stats removed. Before we fixed this
they were 60Mb. Thats holding 30,000 items, and serving a LOT of queries.

Its not neccessarily a NetBSD problem: its just life on a global internet
with bogus users, plus default options to make named.

Why not run named in debug mode and see if you are taking a lot of 
bogus name->address lookups? Not hard to see. Ditto remaking with stats
turned off...

-George