I’m a project manager and have my PMP certification. The reason that I got it is a little different than yours though. I had been working as a PM for 12 years (in pharma), with advanced degrees in science (I used to work in the lab). Only a couple of colleagues at the time had their PMP’s, the attitude among the rest of my peers was “we’re already professional PM’s what do we need this for, it’s useless” (attitude that JimN describes above). Well, my organization suddenly was being acquired by another, and I knew that layoffs would be imminent (most of my colleagues were in that dream-world known as denial on the subject of layoffs). As I began my job search in earnest, I saw that having a PMP was preferred or required in the job description with most of them, so I decided to get one to give me an edge when 15 PMs all hit the market at once looking for work.
If the nature of your work is more on the engineering/production side where process and efficiency are more important, SixSigma/Agile may be more relevant. If you’re managing projects, then a PMP is a wise move. If you’re doing both, then both are relevant. A PMP won’t teach you to be a PM, but will show you what best-practices are and maybe provide you with some tools to use. If you run a project the way they describe, it will take 10 years and you’ll have the bandwidth to run only one. Its one of those things where you give them the answer they want vs. what you think is right.
Getting a PMP is not easy, you’ll need to study every day for a couple of months to get the certification. You’ll take the test in the same testing centers that strung-out and stressed out kids are taking their GMATs, LSATs, and MCATs. If your company is paying, I’d suggest taking a course/bootcamp and the exam right after. If you decide to go the PMP route, hit me up and I can give you some suggestions on how best to study and what tools to use.