Carolyn
I cannot not answer your question on "should" or "should not" rent a vehicle in Sicily. However, I will say the smaller the vehicle the better. I have driven all over Italy, but not Sicily, and never had a problem driving until… it is time to park. If you are going with VRBO make sure your place has a parking spot onsite or close. Finding a spot on the street can be tough! Make sure you brush up on your parallel parking skills.
Of course, driving in the cities demands a little more of the operator than cruising around the island. That is no different than any other location in the world. The only problem is you are in new and unknown territory. We rely on Google Maps and Wi-Fi. While at the hotel/rental we enter our destinations for the day, and it downloads the maps, and we are off. For some reason if the GPS gets lost or goes stupid… well that is a stop for a snack and Wi-Fi to reload.
We will be in Sicily at the end of April and the beginning of May for two weeks. This is our first trip that we did not plan. It is us and 8 other couples touring the island with a chef in our local town who grew up in Sicily and all his family is still there. We are going with two other couples we have travelled with so we decided to fly in 4 days early and got a villa close to the sea and we will just chill. No car required. There is a village about a ½ mile away so we will get some exercise getting supplies.
Good luck on your adventure.
Oh yeah – I did survive driving in Malta, but it was challenging especially with the British cars and road system.