What about first trying to get a job at an architecture office with your commerce / marketing background, there are plenty PR or business development positions available, just to see if your preconceptions about architecture are correct?

I am not attracted to the consumerism culture that characterizes the marketing world

And you don't think consumer culture has bled into the world of architecture?  It permeates ALL aspects of modern life.  Clients aren't building buildings to make the world a better place.  They are doing it to make money.

Whatever you do, don't go deeply into debt.  Please.

Try out some work at an architecture firm.  You can work at a firm without being an architect - try something in marketing or being a business manager.  Or take a CAD drafting class and see if there are any beginning draftsman jobs.  See what it's like for the architects there and get some perspective on the schedule, types of work, etc., It's very easy to idealize this profession, but the nuts and bolts of it (no pun intended) and the realities of firm life can chase away some really talented people.

I second geezertect.  Really take a look at typical salaries/starting salaries and cost of education.  Do the math.  Consider your financial realities (if you have a family to support or don't, if you have other debt, if you have some savings you can rely on, etc.,) and what makes sense for you.  It's really hard to get an architecture scholarship for an MArch and TA-ships only cover so much especially for a major like architecture where you're not just paying for books and tuition.  There is a ton of cost for printing, supplies, laser printing, and other.  If you look at the numbers and you are passionate, definitely go for it!  Just be realistic about what you'll be doing in the profession and what you can/can't afford.

Same as above posts, work in an architect's office or two before you go back to school and take some courses on architecture and design software.  You need to get a sense of what the majority of architects do all day.  

Thanks guys! I will be working on my application for M.Arch, on on the meantime before enrolment (If I get accepted), I'll do what you suggest. How likely do you think an architectural firm hire someone who only has basic drafting/CAD skills and no formal architecture training? I have also been using sketchup for a month or so and wonder if this skill set alone can at least give me opportunities as an (unpaid) intern?