Do it if you are genuinely interested in the subject
And it sounds like you are.

I know a few people with PhDs who graduated around the same time as me (lots of years ago).

About half are not working in the same field that they studied and it hasn't made any difference to them financially but they wouldn't change anything. It might sound a bit patronising but putting off the evil day you leave the Ivory Towers for the big bad world is not a bad thing. Don't get me wrong: they all describe it as financially very tough but they still preferred it to the "real lives" they have now and it's a hell of an achievement to complete.

Of the others some went into teaching where arguably it is a good status thing and helps with promotion. One continued in academia and is now a happy full time lecturer.

It sounds like the subject you're looking at is ripe for future jobs and having a PhD can't do any harm and you'll be insulated from the recession.
(Big Fish Been around since the internet was just fields., Mon 26 Jan 2009, 0:31, Reply)