I haven't tried any other job outside of academia since I started in the field, so it's a bit speculative, but I think that were I to enter the business field, I'd be better suited have gone through graduate training. I think a lot of people who already don't have good social skills go into lab work, and those already lacking social skills certainly don't improve them by spending five years with their head in a book or a microscope. But for the well adjusted, I actually think going through the process of self-doubt and discipline necessitated by finishing a dissertation can be character building, independent of the actual skills learned (which certainly won't be directly transferable to most fields).
I was traveling for work for a couple of weeks, so I've only just seen your reply now. I agree completely with your comments -- graduate training can increase how good you are at other jobs and be character building. I don't think it's a particularly good sole/major reason to go to grad school -- one would probably be better served by working in a particular industry instead, where one can character build and obtain relevant skills.