If you have been to much of the rest of Italy ; I don't know why you would not be excited for a trip to Sicily.
This year will be our first trip to Sicily ; been to Italy about 8 other times.
I am very excited to experience it, the weather for when you are planning should be wonderful including sea temps.
Crowds should be less than in the mainland Italy main tourist areas
Food should be just as good
The ruins there in some cases are older and better preserved than anything in Rome or surrounds
Not sure why you are thinking blah
Have you seen the views from Taormina ; either to the sea or to Mt Etna?
Malta seems like a great add-on but not sure I would dedicate 4 days there unless you are visiting some of the islands that make up the country as well not just staying on the main island.