I've recently finished a PhD and before that a Masters, as a mature student. My advice, in particular re the PhD, would be to have a very clear idea in your mind what it is that you are aiming for in doing it. That could be as simple as "I'm interested and would like to spend a few years researching and thinking about X for my own pleasure"- it doesn't have to be a very grand reason but it needs to be reasonably clear and your goals need to be concrete and achievable.
My experience (and that of a lot of my fellow students) was of going into it with too vague an idea of the point (I mean, the point to you at this stage of your career, not the research questions you look at)- too much "well, I'm interested in the subject and maybe I could have an academic career but I haven't really researched that much or maybe do something else I haven't thought of yet but it would be nice to be Dr X, wouldn't it?" Because it is a big commitment, really big, and there will be times when you think "why I am doing this again?"
So in your shoes I would really look into what sort of concrete professional development you might achieve by doing it- talk to people in your industry, talk to potential supervisors- and really understand how a PhD would improve your professional prospects. (IME academics aren't necessarily great at answering this and tend to assume that a PhD is always valuable.)
To echo a PP, it's not always that helpful a thing to have on your CV, depending on what it is that you do. I work in an area in which everyone has post-grad qualifications and academic qualifications are prized, but even so people are slightly nervous about PhDs and you have to convince them that you won't be too academic in your approach (by which I mean something like "too liable to get bogged down in detail and unable to make a clear decision"- with apologies to any academics reading). At a recent job interview the interviewer only raised my PhD in order to ask whether I thought that was a risk, and I was able to answer by talking about all the bits of doing a PhD that point the other way- teaching, presenting, organising conferences etc- basically downplaying the qualification itself and playing up the surrounding bits.