Salou is a great resort, its got problems such as graffiti but then what town do you know that hasn't got its problems.
I do not believe this resort would have died if the theme park wasn't there as only 5% of Salou's tourists state this is their reason for choosing the resort. Also in 1989 Salou suffered a typhoid outbreak which decimated its tourist industry but the resort was back on top within a couple of years and certainly before the theme park arrived - if it was that bad a resort it never would have recovered.
Its got a fantastic beach (Been to Blackpool & Salou beach is much much much better), the nightlife is good but its no Ibiza and the atmosphere is normally good, the seafront prom is the nicest I've seen anywhere in the world (yes I have been further than Spain)
It is mostly purpose built and won't suit culture vultures but for a cheap & cheerful holiday, Salou does what it says on the tin.
Its the Costa Dorada's version of Benidorm, you'll most likely either love it or hate it, but all the ingredients are there to have a good holiday - If you crave culture whilst there then get the train to Tarragona (10 miles away), Barcelona (70 miles away) and even Reus is supposed to have some really nice parts.
I love it.
Enjoy your hols
Mark