I think buying a car on credit may be an American thing - at least I don't know of anyone who has bought a car on credit. It seems like an absurd waste of money to do so - why not just buy a secondhand car you can afford outright?
Also, paying off (non-tax-deductible) loans essentially buys you after tax dollars, while investments must be bought with pre tax dollars (though some are capital gains taxes if you hold them long enough). That's an additional 15-40% you have to chop off the return rates of investments when comparing them to paying off debt.