You might want to ask this on the WISH boards - lots of marathoners over there.
Anyway, DH & I have done the Race Retreat for the past 2 years.
We were especially grateful for it last year as the weather was freezing before the race. Pre-race it is a very comfortable place to wait (there's a lot of waiting around before it's time to go to the starting line). There is food (bagels, fruit) and drinks (coffee, water, Powerade, soda) and lots of areas so sit. The tent is climate controlled, which was awesome. There are characters if you want your pic taken. There are also several port-o-potties just for the Race Retreat people. You also check your bag in the tent.
Post-race, there are changing areas near the port-o-potties, areas for stretching, massages (can't remember the cost - we didn't do it), and lots of food and drinks. I can't recall the food as I often can't eat after long runs, but I know that DH was happy with the food. There's also water, Powerade, and soda. There are computers so you can check your official time and, of course, characters for pictures!
We chose to do this the first time because it was my first marathon and DH wanted to splurge a little and make it as comfortable as possible for me.

We enjoyed it so much that we did it again last year and we were so glad we did. I think it was 37 degrees that morning and it was really nice to sit on a couch in a warm tent eating a bagel before the race.
If we do the marathon again, we will definitely do the Race Retreat again. However, we didn't have anyone else with us, so we didn't have to worry about meeting up with people after the race.