Hi,
TBH, it really depends on what you didn't like about your undergraduate experience.
Postgraduate students have a completely different dynamic to undergraduate students. They tend to be a lot more grown-up, as in they've "been there, done that" with all the party hard life style. University accommodation tend to separate undergraduates and postgraduates for that very reason (both halls and private housing). Don't get me wrong, they're not complete social hermits, and most universities will have some kind of postgraduate committee / society that arranges things like social events, as well as advice / support for specific postgraduate needs.
The work structure is different as you'll be studying a complete year; without any summer break. Some courses won't have lectures over the summer period but that will be when you're expected to complete a report / dissertation; so you won't have much of a summer... but it IS only for one year (unless you decide to do a doctorate).
IMHO, with more people going to University / higher education these days (and a competitive job market), a postgrad degree will give you an extra edge over those who don't have it. Also, in mainland Europe, they really respect Postgraduate qualifications. The students, themselves tend to be more work-focused... I think because, as you say, many of them are paying out of their own pockets for it... and they want to get their moneys worth.
Also, would you want to stay at your current university or go somewhere different? If it was your uni you didn't like, a new environment will do you good and allows you to make a complete fresh start.
How secure is the Admin job? Is it permanent or are you, say covering someone's maternity leave or sabbatical? Generally, if you wanted a post grad, it's better to do it straight after your undergrad as you'll still have the student / studying mindset; although some may argue that a break from it may do you good.
I know you say you feel bad about your parents paying for it... but couldn't you look at it as a loan? You could agree to pay them back over a period when you're in a full time job with flexible T's & C's. Alternatively, you could look at getting a Career Development Loan (most banks will offer this for post graduate funding, if you can present a good enough case).