A PhD gives you the opportunity to get both a broad overview of a field, as well as delving deeply into some subarea. It will greatly enhance your technical skills and ability to think. Even if you don't plan to have a research career, learning how to do research will be very helpful.

A PhD is a very worthwhile if you don't have anything better to do and if you have the motivation to actually do it.

(Granted, if you are going to dick around for 5 years on a grad student stipend, don't waste your time.)