Do you have any final bonuses to show? Would be interesting to see how it changes how characters are developed.
My guess would be that this change matters a lot for professions that has a single cost high cost in non core areas. Makes it much more attractive to build those categories. For core areas of the professions I think it would change little since you normally double buy these skills and categories.
One thing you might want to consider is changing the penalty for no ranks. In my game I made the change of category progression to 0, 2, 1, 0.5, 0 and skill progression to -30, 3, 2, 1, 0.5. This had the very good effect that buying the categories become optional so you don't end in those silly situations when the player forgot the category rank and thus end with an unusable skill. Not sure if it would change your situation, but I think it is an idea that is worth to consider.