I just returned from our 1st cruise (Enchantment) and I am anxious to get out there again.

My question is whether or not to book it on-line again via RCCL web-site, or to use a travel agent?
I've heard that travel agent's can assist with upgrades, discounts etc. When I booked on-line the last time, we never received any information regarding upgrades, discounts, change in prices etc.
Any advice. We are looking for something in 06', and want to get started paying (we need a payment plan - 2 kiddies).