Karen,
Whether or not you want/need multiple certifications is a very personal choice.
I think that for a 'project management generalist' the PMP is a "must have" in today's day and age. It opens doors, shows that you have the experience and recruiting managers won't even look at your job application without it. But once you have the PMP it really depends on where you are heading. Especially since PMI certifications can only be attained if you are experienced in a particular field.
So you cannot get a program or portfolio certification from PMI without actually having years of experience in the field. The certification shows that you ARE an experience program/portfolio manager. Not that you want to become one. But if you are experienced and focused on those areas and wish to advance your career over time, then by all means get certified. There is definitely no drawback of being able to place those letters behind your name.