I can't comment on Cancun specifically, but we stayed at the Royal Hideaway in Playa del Carmen last May. There was considerable erosion in that area, so would confirm what you heard about the damage being worse further south.

The beach that was left was still pretty and good to walk on, but the biggest problem were these huge black "berms" everywhere, they laid to stop further erosion. They are big bags filled with sand, look exactly like beached whales from a distance. They are about 3-4 feet tall, as much as 20 feet long, get covered with seaweed, and are extremely hard to climb over. They actually blocked the entire beach in some areas in front of seawalls, making it almost impossible to go any further down the beach.