We stayed at Dreams Tulum 7/2-7/7. When I asked the front desk about staying in a "new room" I was told that they did not have new and old rooms. However, they did upgrade us to an ocean view room for $200 in the "old" section. I found the room to suitable for me. It could use a little sprucing up, but it was just fine by my standards. We could literally open the sliding door and we were on the beach and it was very convenient. My sister's mother-in-law stayed at the new section and their room was NEW and very nice but not on the beach. I think your guests will be happy with either section, we had no complaints from the 35 guests that went...that's pretty good considering my family
As for TripAdvisor I would take complaints with a grain of salt...this is not the Ritz but I'm sure some people would find problems with the Ritz on Trip Advisor too. lol.