Interesting mix of replies.
I actually did two site visits; one was piggy-backing onto a cousin's DW, I just visited a few sites including the PDC area. At that time I was already considering Dreams LC.
My second site visit was at Dreams LC, I had already reserved my date and gotten a room block, and got a few nights free as a result of the group block.
Honestly, the only thing the site visit helped me was the food, we got the opportunity to do a tasting and we had surprising results in our decisions. But quite honestly, in the long run, it probably wouldn't have made a big difference. All the food was good, and we would have been happy with what our original choices were. If you're strapped for cash, I'd say skip out on the site visit. It was a nice vacation, and it was nice to bring back pictures to show the guests - it really got some of them pumped up for the trip, but I don't think it's necessary.
I visited 4 resorts total, and it didn't end up changing my mind. I knew no matter what I chose, I would be happy with it, my guests would be happy and we'd have an amazing time. That's all that matters.