Depends very much on your field. For instance, their very useful for careers in the pure sciences, whilst in alot of other fields they don't improve your employability (or wages) at all.
Alot of people say that getting an UG degree improves your wage prospects (and employability) , but if you go on and do a PhD your wage prospects may well fall. At the end of the day, remember that a PhD is a training exercise designed for a career in academia.