Hi Sue! You took the time to reply to my questions on Paphos, Cyprus, so when I looked at your other posts and saw this, I thought that I would try to help you!
We visited Salou 3 years ago, and stayed at the Catalunya Park which is to be avoided at all costs (look at the reviews and you will see why, everything bad said about them is true, in fact some of the reviews look tame in comparison to our experience there!) So thank goodness you haven't booked to go there!
Port Aventura is really fab! We stayed from early morning to close, and could have easily returned again. You will love it. We too, would like to visit the large waterpark one day, it looks great.
We took the train to Barcelona one day. Great day, but it can get a bit confusing when it gets to the underground bit. I was totally confused but we managed to work it out eventually, and then we were fine. We only had a day there, we could easily have spent longer. I can vividly remember the train coming home was very tiring because we had to stand the whole way home, no men giving up their seats for woman and children, I'm afraid (so pretty much like home then!)
I will try to find out if your apartments are near to where we were staying. We had just a short walk over waste ground to a lovely little cove, which was mainly used by locals. We went into the main part of Salou only a couple of times because it was quite a hike - do you know how close you are? Salou seems to be a big place.
All in all, it was a good holiday, apart from the accommodation! We ate at the same restaurant every night - Sun and Moon - just across the road from our apartments.
I shall grill my husband when he gets home from work and post if there is anything else which may be of use to you.
Cheers!
Fi