Rick and Cruise Fanatic,
You're both so right on all points made. There are so many advantages to using your own travel agent, especially if s/he is an experienced cruise seller. For example, on occasion the price of a cruise goes down between the time you buy it and the time you sail. Cruise lines do not call customers or travel agents to tell them the price has gone down. A good travel agent will check your reservation periodically to make sure you're still getting the best possible price. If the price has gone down, the travel agent can request a refund of the difference for you, or get you upgraded to a higher category. This is something your travel agent will keep track of for you. Will a big online site that doesn't know you at all do the same thing? Especially when it means less commission for the site? I don't think so! But your travel agent will do it because s/he wants to do the best job for you so that you'll keep coming back for future trips.
The price doesn't frequently go down, but that's just one example of the value of a travel agent, among many examples, that transcends price alone.
Sometimes big agencies block group space on a lot of sailings. However, no agency can block group space on every sailing of every ship of every cruise line. On top of that, some cruise lines' group price is the same as their individual price, with groups getting other perks, so even if a big agency does have group space, it doesn't always mean they can offer a better price than your travel agent.
Also, in the past, some agencies lowered their prices to the consumer by rebating some of their commission. The cruise lines do not like this practice and have started cracking down on those agencies. If the cruise line finds out that an agency has been rebating commission, they may not allow that agency to book their ships any longer. This has leveled the field tremendously between small to mid-size agencies and their mega-agency competitors, and has also equalized much more the price the consumer will get for a cruise, no matter who he buys it from. Also leveling the playing field recently is the move from cruise lines to offer their product at the same price to all travel agencies, no matter how big or small, no matter how much business that particular agency does with them. Many cruise lines have started doing this and many others are following. The days of mega-agencies getting a better price for a cruise from the cruise line are rapidly ending.
Travel agents not only offer experience, counsel and advice, but they are the cruiser's advocate before, during and after the cruise, should anything go wrong. I'd be really uncomfortable plunking down several thousand dollars to an anonymous online site, but I know people do it.
Shopping around for the best deal is fine, but price alone should not be the only determining factor. Value for the price paid is different, and the value of having the advocacy of a travel agent should not be overlooked.