Dear MBA or Not:
We shall try our best to address your questions but the short answer is "it depends." It depends on your goals, ambitions, and interests and it depends on the colleges in which you can get admission for an MBA. There is not a standard, universal answer to most of what you have asked.
You are not over the most attractive age range for good MBA schools. Good MBA schools prefer candidates who are 26 to 32 years old, with 2-5 years of work experience. Even these schools have students with a wide range on the age spectrum. You can always find colleges that care neither for age nor for work experience; it just depends on how selective the college is. Less selective colleges have fewer and limited expectations of candidates.
No MBA college - no matter how expensive or cheap, or how prestigious or not - guarantees a job upon graduation. It is however true that you have better prospects for superior job opportunities if you graduate from a prestigious college. The cost of education does not figure in directly.
MBA programs in the US, UK, and Canada are expensive. Our focus at iMahal is not on Australia but we can tell you that MBA education in Australia is fairly expensive. For the most part, good MBA colleges tend to be more expensive than not-so-good colleges. Nonetheless, they are all expensive for someone coming from India, due to currency exchange rates. Most MBA colleges offer virtually no financial aid to foreign students.
Your value in the marketplace is dependent on the quality of your MBA education, not necessarily on the duration of the program. Some of the finest MBA colleges in the world are in the US and they offer programs that are 2 years in duration.
What is a good score on your past educational endeavors depends on the prestige and selectivity of the college. This situation is no different in the US or UK or Canada from that in India.
Whether it is worthwhile for you to quit your job for an MBA depends on the cost-benefit equation. In pure financial terms, you must consider the cost of pursuing an MBA against the improvement in your trajectory of progression in your career. Because top-tier MBA schools expect the candidates to have worked for 2-5 years, most people who go there must sacrifice their current career and earnings in the short term, so that they might have success in the long term. They consider it worthwhile to make this sacrifice. Whether it is worthwhile for you depends on your own calculus.
Two founders of iMahal, Joe Judge and Lokesh Datta, gave up lucrative careers to pursue the MBA. They have no regrets for undertaking that path in their careers.