Santa Susanna is nice, not hugely commercialised. Its not over run with us Brits either. Not sure about the weather at that time of year though, especially being so far north.

We stayed there 4 years ago (3rd week of september), its a 4 star hotel and is on the beach side of the railway tracks. its a nice hotel, food ok, but entertainment (indoor) was not up to much, better to walk along to where they have english based outdoor entertainment.
I went to Calella last October (4th week of the month) Weather was not very good, but I have been to Blackpool in October and walked about in shorts and tee-shirt, luck of the draw.
Hope this helps.

Paul