I stay in Swanage a couple of times a year (mainly because I am a steam railway nut).
Kings Road West is on the way out of the town and although it is a main road it is usually quite quiet. It is about seven or eight minutes from the beach, which is wide, clean and safe. The town has lost its way a bit in the past couple of years. The hostelries seem to have gone downhill somewhat and eating out if you want “pub grub” is not as good as it once was. There is a night club at the far end of the main road which can create a bit of noise at chucking out time, but I’m usually well tucked up by then!
The town still has its attractions, though, but I don’t know that I’d care to spend more than about three nights there.