Zaragoza worth a stop?

Yes. In the evening the Cathedrals are luminated and the square is great for an evening stroll. Also great photos can be taken from the bridge of the cathedral. We were there 2 days in Sept 2015. Weather was perfect. Stayed at the NH Hotel and it was in walking distance to square with the cathedrals.

Yes, indeed.
I've made 2 stops in Zaragoza, and would make a 3rd in a heartbeat.
The immense Plaza del Pilar is flanked by a number of historical buildings, notably the basilica with the roof of multi coloured tiles. The ceiling in La Lonja is especially gorgeous, and the Aljaferia ranks after the Alhambra and Seville's Alcazar for its moorish architecture.

http://www.planetware.com/tourist-attractions-/zaragoza-e-ar-zar.htm

I feel it's worth a day and a night. We enjoyed it when we were there.

The summer heat can be brutal in Zaragoza.

If you are counting on seeing it illuminated after dark, you'll want to spend the night. Sunset's around 9.15 in early August.

Thank you so much! I think we will definitely spend at least a night there.

Thank you so much! I think we will definitely spend at least a night there.