Recent economic history has done a good job of demonstrating that people can lose their heads during asset-price booms, assuming that prices will keep rising forever and overpaying for assets as a result. That being said, it also seems probable that people overreact to asset-price crashes. Given the hammering stock values have taken, it seems probable that there are some good deals out there: companies that have strong business models and future prospects, but which have shares trading cheaply due to excessive pessimism about the markets as a whole. It is certainly a bit strange that people treat stocks as an asset where you buy fewer when the prices are low, while treating almost everything else the other way.
It might not be a bad strategy to make a few guesses about firms that are in this situation, buy a modest amount of stock in each, and then simply refuse to look at the value of the shares for five years or so (to avoid getting depressed by medium-term losses).
I suppose one nice thing about concentrating on the repayment of student loans is that you don’t need to worry too much about making investment decisions. Getting above the water’s surface is a more urgent task than investing for the long-term.