I have made a rare foray out of my lurker cave to answer this one, as I did a PhD some years ago.
I agree entirely with magi22 and Amber. Ideally, a PhD is for you if you are so interested in your academic subject that you can't imagine doing anything else. It is pretty-much essential to do one for an academic research career. Some companies ask for a PhD for promotion to higher-level posts, but I do wonder sometimes if they are expecting something magical and unrealistic that does not correspond with the reality. In science, which is my area, a PhD does not generally teach transferable skills such as management, commercial awareness or ability to negotiate. You might, along the way, improve oral and written presentation skills, and learn to manage a biggish budget but, fundamentally, it is all about the nitty-gritty of advancing a fairly narrow area within your subject.
It is not necessary to be a genius to do one; perhaps it was a century ago, but the number of PhD students has increased massively in recent years. You do, obviously, need to be quite bright, and to have a good degree, but passion and determination are the most important things. Supervisors vary, and some PhD students end up unsupported and disillusioned, though this was not my experience. Universities are starting to be more professional about the way they look after their postgraduates, e.g. using auditable records to show that supervisors hold regular project meetings.
There is debate over the possible financial advantages. It depends where you end up afterwards. Academic salaries are not huge, though better than they used to be. One danger, I think, is that of following the PhD route, finding that you no longer want to pursue a related career, and having narrowed your options to the point where you find it difficult to do a different type of job. Also, be aware that the academic job market is hideously competitive. Only a small proportion of those taking up temporary post-doctoral contracts ever get a permanent post in a university.
A PhD can be exciting and rewarding, but do speak to other students of potential supervisors carefully beforehand, and think hard about why you want to do this and what you expect to get out of it.