Punta del Este has long been a European hotspot for beach time during the winter in the northern hemisphere (seasons are reversed of course), but it has it's charm in the fall and winter as well (spring and summer in the northern hemisphere). We found ourselves visiting Argentina and Uruguay in May. The boat ride from Buenos Aires to Colonia is magnificent and it is a nice bus ride along the coast from Colonia to Punta del Este.
Prices here are much cheaper during the down season (it can be quite expensive other times of year) and there are no crowds. Temperatures are too chilli to get in the water (although we did see some surfers catching waves in wet suits) but still perfect for walks along the beach.
We rented a scooter to explore the all of Punta del Este and the surrounding areas. We found a beachfront condo on the cheap.