Not worth a whole day in Monaco - a few hours tops -if you only have a week on such a great route. Even Cannes can be done in half a day. Nearby Antibes also worth a couple of hours.
If you had whole week in provence then worth spending longer in the above and many other places. But not when you have to get to Barcelona by such a attraction-filled route..
not sure if you're travelling my car or train. You don't have time to do any of these places justice, so you may have to skip a few. AixenProvence, Marseilles, Arles, Narbonne ( Plus side-trip to Carcassonne).
After Perpignan, (o.k. but not great)head for coast -Port Vendres- stick to coast for beautiful Costa Brava drive and at San Fileu head inland to Girona before arrving at Barcelona.
Whenever I plan these trips my wife cuts them in half and says she isnt spending all day every day touring around, visiting cities and scenery and ending up exhausted whilst i dig up another boring fact about such-and-such a place. My teenage daughter will have jumped out of the car after one day.
So it depends on whether you are travelling with family , or whether you want to enjoy yourself!
this is a great route -whether by car or train. Worth planning.