This might not be the kind of answer you're looking for, but the best way to truly passively increase your wealth is to take care of your personal finances (e.g. pay off your student loans, pay off your credit card balance, invest in a lifecycle fund, see if your employer offers a 401(k)) I personally really liked the book I Will Teach You To Be Rich -- it has a poor name but it's dense with incredibly practical advi…
I support the idea of paying off debt. 401k (investment groups) however, is essentially giving your money to a gambler, and having him play your hand. Bet on yourself. Always.
IMO, the best approach is to spread your bets. Obviously getting rid of debt is the easiest first step, and 401k plans are less-than-ideal because of the restricted investment options, but you can minimize the gambler's influence by choosing index funds (if you have the option).
The stock market itself is a gamble, of course, but so is just about everything else, so minimizing your exposure to any one risk is the best you can do. I've been in dividend stocks for years and making $500/month or so with minimal exposure.