I' a big fan of the whole dinner with a view thing (who isn't?) and the west coast of Portugal seems to be perfect for that. Just pick a random spot (that's excatly what we did, no planning ahead) and you're likely to find a restaurant with the freshest seafood and an ocean view. Best thing ever!
Douro Valley is at its best off season - I went there last October and would definitely recommend this place for a fall trip. Get ready for postcard-pretty vineyards (famous for they ports, but pretty skilful when it comes to other wines as well), delicious food and picturesque views. Stay in one of the charming vineyards and spend your days on walks in the vines, scenic drives along the river and picnics on the hills.