Well, unfortunately, I haven't seen much of Portugal, but while I was studying in Seville, some friends and I took a weekend trip to Sagres and Lagos. I loved looking over the cliffs at Sagres, though the weather for us was horrendous and rainy - I hope its better for you. Lagos was pretty neat, though we didn't go down to the beach for bad weather. It is mostly European tourists. We spent most of our time in an Pub ran by an English family that has every currency I can think of hanging behind their bar and an Australian surfer bar. It wasn't a place I would characterize as wonderfully rich in culture. Very Touristy and expensive ( at least for a starving student) but we found a wonderful apt. to stay at for the few nights we were there for a good rate. Apparently that is a common way to find reasonable lodging and in Sept, I don't think it should be so crowded as it usually is..
We did love that English pub though, In fact they took a picture of all of us, a friend of mine is carrying me and told us they would hang it up on their bulletin board. I wonder if they did. I also shot my best billiards game ever and they had good food - They bragged about having the best hamburgers ever, but as I am a vegetarian, I didn't get to judge. I'm not sure if you have experience driving in Portugal or not, but watch out in those narrow streets. We almost lost a mirror! I'm sure you'll have a blast. Cheers! Hope this helps.