I have checked it out and this is what I found as the basic upgrades; and it costs $25. a year:
Increases storage space from 10,000 images to 50,ooo;
Increases image file size from 1MB to 2MB;
Increases image dimensions to over twice as large;
Increases length allowed for a video from 5minutes to 10min;
Get a 10% print discount.
Overall I feel that it is called PB Pro because it would be a good deal for PROfessional photographers, or others who work a lot with their photos.
It has nothing going for it, for me, and I wouldn't spend my $25 dollars for it! It isn't an 'upgrade', it is a 'purchase'. I just never go there, or delete whatever pops up from them for that.