WAL tuning advice

I'm hoping someone can help me figure out how to better tune my WAL parameters. Right now I am seeing WAL activity that is faster than I think it should be - we average about 30 write queries a second at our peak, and yet we're getting a new WAL file every 15-20 seconds.

Our postgresql.conf parameters:
wal_level = hot_standby # minimal, archive, or hot_standby
checkpoint_segments = 10 # in logfile segments, min 1, 16MB each
checkpoint_timeout = 5min # range 30s-1h
checkpoint_completion_target = 0.9 # checkpoint target duration, 0.0 - 1.0
#checkpoint_warning = 30s # 0 disables

Here is "select * from pg_stat_bgwriter;"

checkpoints_timed: 2081;
checkpoints_req: 18889;
buffers_checkpoint: 4320036;
buffers_clean: 416180117;
maxwritten_clean: 1580518;
buffers_backend: 77676446;
bueffers_backend_fsync: 0;
buffers_alloc: 4804432940;
stats_reset: "2012-06-24 23:13:10.716096-04"

From my previous research, I *think* that that data implies:
1) Due to high ratio of checkpoints_req to checkpoints_timed, I should increase checkpoints_segments, maybe from 10 to 15?
2) There are only about 206 buffers (buffers_checkpoint/(checkpoints_timed+checkpoints_req)) for each checkpoint. I think that is far lower than it should be, but I'm not positive about that, and I don't know what would increase it?
3) maxwitten_clean should be much lower than that?

Thanks for your help!