I actually lived in the Voltacentre for a while - I would concur. I wouldn't live in Basel at all - but especially not in St. Johann. I would also particularly avoid the Clara area, especially with kids (full of sex workers).

Personally i'd live in Rheinfelden. Much nicer than Basel, lower taxes (in Aargau), well connected (less than 10 minutes on the train). There's an international school there too.