Don, thanks for the prompt response. I've created both postgres and nsadmin users for the new db. The peer authentication failure occurs at (it appears) the *last* line of the dump file, not the first, since it is the *last* line in the std error redirect file following a whole bunch of NOTICE: CREATEs but no ERRORs. (I get no errors during the original pg_dump of the first database, too, FWIW.)
For no particularly good reason, I've dropped both the postgres and nsadmin users for the new db and re-added them. I still get the same problem, only now the authentication failure is for user 'postgres'. Does the dump file carry info about permissions that isn't clear?
I also tried the -d -D flags with pg_dump and have the same results: the schema gets imported but none of the data, with the same peer authentication line at the end of the error file. Hmm...