Note: all salaries here are rough estimates and relevant to the UK job market.
IIRC in the UK you can expect to earn about £15k while doing your PhD and immediately afterwards, and I know of fully fledged middle-aged Professors with 35 years experience who are barely scratching £40k. If you'd followed a path into live industry, you could be earning £65k plus by this point. Newly qualified stockbrokers in London can earn £40k as a starting salary which may put this into perspective for you. Also, there's more to computing than programming as well, you know.
I would like to also say that these research papers that are submitted by academics are usually regurgitated, opinionated shite. If you look at the reference list, it's usually about eight miles long and referencing other people so you have to ask yourself about how much of it is truly original, groundbreaking stuff. Fact is, that stuff is a load of bollocks to outsiders and the uninitiated - academics tend to be a very tight-knit, closed circle and I've seen very little of this stuff actually coming out into a live workplace.
To put my (very misguided and likely to be wrong) opinions in a nutshell:
- Don't do a PhD to become an academic if financial stability is your goal (which you alluded to) - teaching is difficult, time consuming and often thankless work and the pay is usually pretty low in comparison to the other things you could be doing
- By all means do a PhD, but it's an expensive and time consuming option and, IMO, some of the theory and things you do will be esoteric, beyond the scope of non-academic work environments and an employer may look down on it
- If you feel that a PhD can enhance your employability, ensure that what you research is directly relevant to current or mid-future trends
- The time you spend on your PhD may be better spent doing some kind of internship or training that makes you more employable - because, let's face it, the Financial Golgotha won't last forever; the job market will re-open and it'll be dog-eat-dog's balls for the new jobs that do appear so you need to stand out. The days of waltzing out of Funkytown University and straight into Faceless Conglomerate Ltd.'s Graduate Program are over for the time being
- Maths is a tool to be used in conjunction with other tasks and I fail to see the value of studying it for the sake of it. Would you do a PhD in screwdrivers and never do any DIY?
Take my opinions as you will: I am very materialistic and believe in anything which can turn a profit.
That said, many employers value diversity and a wide range of (not necessarily) academic interests so it may or may not benefit you. Mind you, a PhD is a very expensive and long-term commitment here for three years, so you'd better be sure of what you're doing before you start.