Portraiture is $200. Portrait Professional is $40-60 (32-bit). I've only used Portrait Professional so am not qualified to comment on the more expensive software, but I would expect it to be faster and easier to use, and capable of better results.
It might be that if you use a software like this X hours a week, or on XX number of images weekly (fill in your own numbers), you could justify the more expensive software because of increased productivity - the ability to improve more images to your (or your customers) standards in a given amount of time.
Otherwise, I've found Portrait Professional very capable of producing excellent results.
Both of these images are processed with older versions of PP; the current version 10 produces even better results (easier to control, wider range of effects and skin textures).
Other than being a registered user of Portrait Professional (for which I paid full price) I have no affiliation with the maker of either software.