improving performance with more -B buffers?

I've got a table with about 425,000 rows; it takes up 90 MB and
there are several indexes on it (together taking up another 80 MB or so).

Most queries are in general pretty fast but some of the queries,
as reported by "explain", do serial index scans and take a few minutes.
During these queries the system is very much I/O bound. The machine this
runs on has a very fast disk subsystem (DPT RAID controller with 4MB cache,
talking to ultra/wide Seagates) and lots of RAM.

Aside from adding (or changing) indexes to the table, can I improve
this kind of performance by adding more -B buffers to postmaster,
or won't that really make much difference? There isn't much concurrent
access, and most access is read-only (only one daily update).

Thanks,
-T.