We did, and here is our experience...
Getting a taxi, no problem although our driver got in a fight with another driver right before he took of and was driving angry. It was kind of scary, we were in one of those safari-type vehicles where you can't talk to the driver. The way back we had a better driver. It was $28 for the 3 of us to get there and he did not get a tip as we were thankful just to have lived through the ride!
Coral world was so lame, in our opinion. If you have ever been to any aquarium this will be a disappointment. It was dirty and we discovered so many more fish snorkeling. There were iguanas and wild chickens roaming everywhere, but this is throughout all of St Thomas. They had a little sea lion show and the trainers were so rude, yelling at babies and little kids for making minimal noise.
Coki beach, however was beautiful! We wish we had the 2 hours we wasted at Coral world for more snorkeling and beach time. The fish were awesome, and it was only $10 to rent equipment. Had a nice rum punch on the beach. We did use the bathroom facilities at coral world but they had them on the beach too.
If I could go back, I would skip Coral World and just go to the beach. Have fun, whatever you choose!