I am of the opinion that you do PhD for the love of the subject.  If you want to do doctorate in Comp. Sci., you should do it because you are truely interested in exploring and transcending the boundaries of that subject matter. 

But sure you can make tons of money after getting PhD.  Being a professor after PhD is not your only option.  With the new tools and experience you have garnered during your tenure as hardworking doctoral student, you will fetch much higher salary level.  Unless your research work is extremely esoteric, you could bring to market what you have been doing in the academics.  Your starting salary could approximate $150K in certain parts of the country.

But more than money, I would say it is the personal satisfaction one gets from achieving the highest academic degree in your chosen field.