LAPP server moving from 4 GB RAM to 16 GB - increase shared_buffers?

Hello,

I run a LAPP server (PostgreSQL 8.4 @ CentOS 5.7 / 64 bit;
only 4 GB RAM) with the following config:

postgresql.conf (unix socket only and - ):

max_connections = 50
shared_buffers = 1024MB # min 128kB

pgbouncer.ini:

[databases]
pref = host=/tmp user=XXX password=XXX dbname=XXX

[pgbouncer]
logfile = /var/log/pgbouncer.log
pidfile = /var/run/pgbouncer/pgbouncer.pid
listen_port = 6432
unix_socket_dir = /tmp

auth_type = md5
auth_file = /var/lib/pgsql/data/global/pg_auth

pool_mode = session
server_reset_query = DISCARD ALL;

server_check_delay = 10
max_client_conn = 200
default_pool_size = 16

and httpd.conf (running Drupal 7 + custom PHP scripts,
non-persistent, with mostly "select" queries):

<IfModule prefork.c>
StartServers 8
MinSpareServers 5
MaxSpareServers 20
ServerLimit 120
MaxClients 120
MaxRequestsPerChild 4000
</IfModule>

It works ok, but now users have collected some money and
I've purchased a better server with 16 GB and CentOS 6 /64 bit.

I understand, that my question is naive, but on the other side
even if I provide more information, will that really help? -

My question is: should I increase shared_buffers
from 1024MB to 8192MB, does it make any sense?

Thank you
Alex