I was asked for input, the following is my response. If anyone else has anything to add then feel free to chip in.
When making a long term investment, you should first consider the cost and the pay out. If you're considering starting your own business, you should see other businesses selling similar goods and takes notes on how they sell goods, what is their customer base, is there room for improvement, and what is the real profit center for this business. Warren Buffet never invested in the tech bubble because he couldn't understand how the profits were driven, his methods were praised when the tech bubble crashed. It's necessary to understand the business because doing so enables you to see whether your strengths and weaknesses are a good fit for the type of investment you are going to be making. It's not so much as wanting to do the business as it is seeing you actually operate as a professional, still retaining passion, and understanding how the system works so when things change you are aware and can adapt accordingly.
If you already have debt then you shouldn't invest into something that has a low success rate. If you have expendable capital or can qualify for income based repayment to soften debt then you can carry on a bit more risk. However, you have to ascertain how much you are paying to take this % risk, what are the pay outs, and plan how taking this risky venture will be executed so that it leads to pay out instead of falling to entropy. Also, always have a Plan B. Even if your Plan A has a 90% chance of working out, take as much leftover energy as needed to make sure there is a solid Plan B that has an even lower chance of failure to pad the fall. To help you ascertain success rate I would again poll people in the industry and ask them the hard questions. Try to figure out what percentage makes it and also if there were people who washed out. Try to understand how other people didn't succeed and tell them that you're interested in pursuing a similar line of work. Take all opinions with immense scrutiny and because you have the privilege of being an outsider, try to profile why they believe certain outcomes will lead to a solution or would have lead to a better future for their career and business.
In the process of research, connect with people and express an interest in maintaining contact. They may be your next employer or may lead you to the next employer. They may even be your Plan C when the cables come lose. Choosing to invest in further education in this context is a business decision. I will tell you that in our current field of studies, our area of major has a bimodal pay out. Putting in another four years for professional schooling makes an enormous difference in pay out, along with harboring more debt. However, there is little room to grow with only a B.S. in most companies because they are not expanding and have relied on insular methods of employment requiring long years within the company to climb and more likely than not a higher accessory degree is going to be favored when reaching a professional peak. Physicians are an extremely diverse field with numerous entries of acceptance. If you can make it to an allopathic school then you match rate is above 90%. However, your chances of matching into your specialty of choice is highly dependent on how well you do in class. Therefore you have a proportional chance of working in a specialty you never saw yourself working, but chances are you will make enough to live comfortably. Going for a Ph.D has a more variable pay out depending on the rigor of the school, the opportunities that are tied to the school, and figuring out how this Ph.D will enable you more than the B.S.
Academic jobs will rely on you applying for grants from the government and seeking funding as well as staffing your labs and supervising research. Your research will be oriented towards bringing profit or some type of benefit to humanity and convincing investors to put money into the pot for your idea. With a Ph.D you can also work for big time corporations i.e. Merck, Pfizer however the 1990s have passed and the tone is more about doing more with less, than getting more for more. If you go on their career page you can see what type of skill background they want from Ph.D candidates to take on jobs at the company and the type of positions they envision their Ph.D's to fill. This is a great area to network and ask how people who presently hold jobs got there and to make a plan on how you're going to structure your education and internship opportunities to place you within a position of choice.
The best person to address these questions ultimately comes to yourself. Assessing yourself, your value, and what value an M.D., Ph.D, or whatever future degree you are considering will add human capital and investment capital allows yourself to plan and project yourself in interviews rather than leaving 'hard work', 'passionate,' and 'willing to grow' on the resume as questionable variables for employers to consider. You are your strongest supporter and self-advocate and if you don't take a leading position then someone else may steal the position all together. It's not surprising to be concerned given that everyone is focused on the economy and jobs contracting. However, fear has always been a part of the American stimulus. Whether we fear our neighbors being Nazis, being drafted to fight in Vietnam, or terrorism in our country there is nothing to be gained by trepidation of the future except for the subsequent angst of not taking action to address it sooner.