@Immanuel Sibero -- Dr. Mueller has some fantastic material on economic trends. Here is a link to some of his work if you're interested in the technical side of market analysis: http://ashworthpartners.com/3-things-i-learned-charting-multifamily-cre-market-cycles/
I would say that if you're buying apartment complexes for the appreciation, however, you're likely in the wrong market. Sure, you may be able to force appreciation in an apartment building by raising rent, having tenants pay utilities, etc etc etc, but when you sell an apartment building, the capital gains taxes and realization of depreciation absolutely cripple any profits you might make on a sale. The best apartment investors I know live by one rule: never sell. For most investors, SF is the vehicle of choice for capitalizing on appreciation and market trends as it will likely result in a higher net worth over time.
My rule of thumb: buy single family if you're interested in playing a more active role in analyzing and capitalizing on market trends (buy high, sell low) and if your goal is net worth. If you're buying for cash flow, then buy multi-family and you can often afford to ignore minor changes in the market. The consolidated management costs and the scalability are far better than purchasing single family homes when your end goal is cash flow (think of all the Six Sigma wastes you eliminate by consolidating everything for 30 units worth of income into a single transaction).
Also, @Immanuel Sibero, I know some will disagree with me on this point, but in my opinion, if you buy an apartment building with good cash flow, who cares what the cap rate is? If you're interested in cash flow, you're not going to re-sell it anyways. Buy at the market peak as long as you can see a good cash flow from Day 1. There's no real need to sit it out on the sidelines unless you're trying to play the market, which again, is better left to those that are playing with larger sums of money or the SF market.
@Jesse Chunn, it sounds like you want to gain $20,000/mo of rental income. Since you don't sound like you plan to buy and sell, the tradeoffs you take with SF homes likely won't pay off because apartment complexes are by far the best way to leverage your time and money for cash flow. You're not buying for net worth, you're buying for cash flow. Buying apartment units with slightly lower than average rental prices will shield you in the event of an economic downturn as people always seek cheaper rentals during those times. The SF market will hurt during a recession while a good middle-of-the-line apartment building will likely always have demand (though it depends on your area of course).
Would love to hear how everything turns out for you!