I was kind of surprised to see that Sicily was omitted from my older copy of RS Italy. I went ahead and bought the Sicily-only RS book. But I really feel this book needs some refreshing.
TRAVEL MODES :
For starters, the only travel modes seem to be to fly into Palermo, rent a car and make a circuit. I have been to Sicily three times and I never flew into Palermo nor rented a car. What I did was fly into Catania, take a train from mainland Italy to Messina, and take a ferry from Naples to Palermo.
I have decided not to rent cars in Italy anymore after a few bad aspects a few years ago (getting 400 eu in fines for driving to the city center in Bologna without seeing any signs preventing it, and looking for gas stations on google maps, to find no gas station, then finding one and putting 20 eu into an automated system, and driving off only to find that it took our money but did not pump any gas actually, plus some hair-raising experiences on buses on narrow roads).
You can get around via trains and buses. And there are several bus lines apparently (Etna for example) and one with an app (SAIS), etc. For example, you get a bus from the Taormina city center (up the mountain) straight down to the Catania airport, or from Ragusa to Catania in half the time as the train.
A guide book should offer a few options and alternatives. Not just one option.
BUDGET UPDATE : I have not checked the actually hotel recommendations but I can tell you that I paid around 60 eu in January 2020, and now same places are 3-4 times as much, less than 3 years later - but that is happening all over Italy. That affects your budget a lot.
HISTORY : RS does touch on the Arab, Norman, Greek, and half a dozen or so other conquerors. But having read an entire book on the history of Sicily, the history is much more deep and interesting than that - and perhaps no place in Europe has a more varied and interesting history.
There was a slave revolt against the Romans, and battles of the Punic wars - including the massive naval battle just to the south of Sicily that destroyed the Carthaginian fleet. There was the famous rivalry between Montgomery and Patton during WWII and their race to Messina. There was the massacre of a Norman army at one particular place.
Siracusa was the home of the foremost mathematical genius of the ancient age, Archimedes. Your might recall the "Eureka" story when he discovered density in the bath and ran through the streets to prove the king's crown was not pure gold. Its also the location of the Roman siege thwarted for a time by Archimedes parabolic mirrors which torched the Roman ships (the precursor of today's satellite dishes), etc.
The details of the Norman rule, and its acceptance of Greek and Arabic is amazing cultural flexibility for that time.