We were just there last Sunday(10/10). Great day to go: no cruise ships & many of the vendors were closed. Just ignore the ones that are there as suggested by the bus driver. Don't forget your water shoes...they are a must! Enjoy....its a great experience!
Another bit of advice about Dunn's River, ask at Guest Services which day is not a cruise ship day, and go on that day. You will enjoy it a lot more when there's not crowds of people there from a cruise. And yes, do it! It's something everyone should experience!
As noted above, guest services will have an updated list of days with no cruise ships, and I believe Sunday is always cruise-free. I would suggest when you're done, you sort of duck out the entrance instead of going through the "official exit," which will herd you through a "craft village."
I'd also suggest not keeping money in shorts that become transparent when wet: I did that, and I ended up buying some bead necklace. (I could have been a B*&^# about it and kept up my very obvious I-have-no-money-on-me lie, but the guy did make me laugh, and it was only a couple bucks, so what the heck.)