A few years ago, I used Erice as a base, and loved it. Very beautiful, ancient and special place, particularly in the evening and early morning, when it was very misty, mysterious and memorable. Great food in town also. One day I drove from Erice to Segesta, had plenty of time there, then drove to Selinunte, had plenty of time there too. Then I drove back up the coast, planning to stop and visit both Marsala and Trapani, which I thought of as mid-sized towns. I found they were both very congested small cities, with heavy traffic, absolutely no parking that I could find, and dreaded ZTLs. In each place, I ended up leaving without even stopping, and just felt lucky to find my way back to the highway without a fender-bender or a ticket. When traveling to either Marsala or Trapani, by car, I highly encourage people to have good city maps in hand.
Note: by the way, at Segesta I started at the temple, then rode the shuttle bus up the hill to near the theater. I had intended to take the bus back down, but found it had left while I was taking a photo. Good thing, as the walk back down was wonderful. The view of the temple changed greatly as I walked down the hill and it was closer and closer, with just green forest and hills in the background. Beautiful and varied photos along the way.