I stayed in Playa el Agua March 98'. To answer your question on crime, I found it to be safe. My girlfriend and I both walked day and night long distances and felt very safe. Of course, always follow common sense. Our walk at night was due to getting off the bus at the wrong stop. I didn't stay at an all-inclusive, therefore, we ventured on bus, frequent and convinient, to the local capital Miramar. Once in Isla Margarita don't expect to be pampered like tourists are in other destinations.
Everything is very laid-back there. Also, be warned that jelly fish ruin the beach at certain times of the year, ex.March. The locals say they don't sting but I did't take their word for it. One last note, prices are almost the same as here in the U.S. for food and drink, the bus is very cheap and easy to understand, very few people speak english, so learn some Spanish if you don't know.