went in October last year and staying at the Dorada Palace.
Port Aventura is great with the halloween theme. parades on Saturday night which is cool. We went early in October and generally the park was really quiet you could stay on rides and go round time and time again. Definitely worth buying a 7 or 14 day pass in advance. Costa Caribe was poor. We got a day included in our pass for Port Aventura but think they have stopped this now. The waterpark in La Pineda closed on 14 October last year so probably earlier than you'll be going.
weather was hit and miss. First few days bright hot sunshine. definitely in the 80s. Then almost a week of rain! But never cold. Then more sunshine
However the resort was closing whilst we were there. Bars like Kiss and some restaurants were boarding up their windows for winter. I'd say about 25% of the resort was closed by the time we came away in the third week.
it was a bit disappointing with the weather, but we were in a nice hotel and went to Port Aventura all the days it rained. You strap on your poncho you get for the waterrides and just get on with it!!
We got an absolute steal of a deal and its a no brainer - I would definitely go back to Salou anytime, and I'd still give October a whirl cos there's so much to do. train to Barcelona etc
Rich