Hello Andrea,
I agree with kathrynj... it's too much driving and check-ins and outs for 2 weeks but, on the other hand, those are all amazing places ;) It's true that taking a train to Coimbra is really easy but you'll be more dependent on schedules...
I'm from Porto area and I think you could use your extra day for a day trip to Guimarães and/or Braga (both north of Porto)... Guimarães has a wonderful historic centre (including a castle and a ducal palace) that is listed as UNESCO's World Heritage; Braga has some beautiful churches and sanctuaries like Bom Jesus and Sameiro (if you're into religion).
All in all, if you like driving and money isn't an issue, I believe your itinerary is great... I'd leave out Nazaré and enjoy a little more of the other places but other than that, it's great ;)
Enjoy Portugal, I'm sure you'll love it ;)