“How does earning VIP points work when using your existing points? For example, if I were to buy Hogwarts at £350 using my existing £90 of points, would I earn the full £350 worth of points, or earn £260 worth?”
I think it is 8 points for every £ you actually spend (not including points used). So £260 will be 2080 points (or 4160 during double points). I tend not to use my points during double, so £350 x2 will be 5600 points to spend later.