Genoa is 3 hours by train from Nice, less driving on the highway ( toll, lots of tunnels).
Drive on other roads - by the sea and through small towns - is beautiful but can take hours ( huge traffic).

I still can't make up my mind about whether to rent a car for my 5.5 day trip coming up in July.

Car rent plus parking near where I would stay would come out to about $400-425. Not bad and I wouldn't have to spend money for transfers to and from NCE airport when I arrive and leave.

It's when I have to park to go to places like Antibes, Villefranche, Villa Ephrussi de Rothschild, St. Paul de Vence (Fondation Maeght used to have free parking didn't it?), Eze, Monaco.

Not to mention toll roads. Years ago, I rented a car in Nice and went as far west as Pont du Gard (north of Nimes) and as far east as Monaco and north of Nice to some of the villages (where there were no crowds). Tolls weren't that bad nor was the gas.

I don't mind trains or buses but getting to stations could take some walking.

I could be ambitious and think of places like Ventimiglia as well as St. Tropez and Gorge du Verdon with the car.

Maybe best to reserve the car now and plot the itineraries later.

We're staying two nights in Saint Paul de Vence (Le Hameau)--with all the traffic and construction, would you recommend having dinner in Nice one night, or is it a scary ride back at night? I know it stays light until 10.

Stu, any restaurants in the area you recommend?

I'd forget about the car since you're going for less than a week and traveling in the month of July. Nice has very good train or bus connections to all of your destinations ( except St. Tropez, which I think involves a boat and bus combination). Travel in and around Nice in a car is a total nightmare in July. Trust me. I've been visiting the area on and off for nearly 20 years in July/August.