Will be spending a week in late April at Frenchmans Cove in St Thomas. Is a rental car desireable/needed?

This is one of those questions that doesn't have a right or wrong answer. It all depends on whether or not you plan on leaving the resort to explore the island, how often you plan to do that, and, if so, whether you are comfortable driving yourself or would rather take taxis. The one thing you should knows that using taxis as your primary means of transportation can get expensive and if you "travel a lot" or go long distances r/t fares in a taxi can cost more than daily rate for a rental car.

For what it is worth, I travel a great deal all over the world and almost always get rental cars wherever I go.

If your read various trip reports (especially written by those visiting the Caribbean you'll find you rarely head about someone regretting renting a car but you will often read about how expensive taxi rides are. So it all comes down to how YOU view your time. Having a rental car at your disposal will allow you to come/go as you please. Using taxis will limit your movements and be subject to the availability of taxis where you happen to be at the time they are needed.

Thanks RoamsAround. Have been to a number of islands and usually do rent a car. Because St. Thomas appears to be smaller than most of the other islands I
was considering the rental question somewhat form size of the island. I do agree with all of your comments about general expense of taxis in the long run if you
do plan on moving around to any significant degree.

Skip: The taxis charge per person,so if you decide to go out to dinner from the Cove, you are going to have to add on $20+ for two people. St Thomas may be smaller than many islands, but "you can't get there from here" a lot!