Was there during the day about 2 years ago, now admittedly it was a bank holiday Monday, but I never felt so threatened in my life (and this is from somene who walks the streets of Limerick....

, just messing Limerick people, its a badge of honour thing !!). Place was jammed with knackers, many of them legless drunk.
That said I'm sure mid-week in September and not being out late nights you would have a grand time.
As an alternative, but along the same lines, you could bring the car to Rhyl in North Wales. An easy drive from Hollyhead, no baggage charges, bring loads with you and home again, probably cheaper on the ferry as compared to 4 flights, taxes & baggage annoyance.
Rhyl has the same 1950's seaside holiday "charm"/nostalgia but is not quite as run down or rough as Blackpool. It has the sun centre (looked quite good - peered in the window, was late in the evening). Fine big beach - though personally I like more sheltered beaches - and a really well redeveloped beach front. Cracking curryhouse. Does have some derelict building and the fascination with slots machines, though neither to the extent of Blackpool.
Its also near Chester (about 1/2 hour away) which is great for shopping (retail parks) or olde worlde town centre touristy ramblings. Plus you are near Liverpool & Manchester if you want to check out sights, shopping or soccer matches/stadia.
So if you were willing to drive then Rhyl, as a base, would be my pick over Blackpool.