@Nimmott: Take the postbac and then do apply for a masters since your reasons for doing so seem solid. Don't worry about being an older person on campus, you bring a different perspective than the rest of us so adcomm's will consider that. Also your sop for admission should tell your story of why now really well and I think your age and experience can actually be made to work to your benefit. A career shift is a great thing to go back to school for. All the best.
Regarding the PhD: Unless you'v saved a ton of money and don't mind spending it now to make yourself comfortable, IMHO you are a little too old for a rigorous PhD programme because you have to go back to living so cheap. If you can afford to make yourself comfortable though, I think you should go for it, if not for anything else to get rid of that ABD that seems to be nagging at you. Of course the academic preparation you would have to do to be competitive is going to be quite crazy
If you finish your masters degree I don't see any reason why you should have a dip in salary. Your experience in technical writing will still count vs a fresh graduate student with lil-to-no experience.