You should try to spend at least one night at the Bussaco Palace Hotel for a really romantic evening. They have a great restaurant, great wine cellar (along with exclusive Bussaco wines)and the staff was wonderful to us when we stayed there one of the days during our honeymoon in 1985.
The link below gives a description of the hotel (I'm not recommending the site, but it has a good description and pictures)
http://www.europeforvisitors.com/europe/articles/bussaco.htmWhile in Lisbon you should take side trips to Sintra (castle) and Obidos (great walled town)