Wife and I did a renewal last march. There were around 26 or us in the group, the price was more than worth it. We went for the hor d'vorse (sp?) and 1 hour of drinks to go with it, and I still think it was worth it.
The down side, you have to use the Carnival photographer, and he/she is going to want to monopolyze your time getting photos (and selling them to you a few days later). We did end up purchasing the photos, which was more than I wanted to spend, but since the wife and I did a JoP wedding the first time around we figured it was time we got some real wedding photos anyway.
All in all, very much worth it. and if you have a large group going with you opt for the small reception to go with it.