As you accumulate more properties and get more appreciation, principal paydown and cash flow it becomes exponential.

Once they shack up with a significant other they start to accumulate too much stuff for the space.

We accumulate some rentals but mostly do flips.  

may be the most profitable "right now" task.That said, you will probably quickly accumulate some capital.

Suppose my goal is not necessarily cash flow (say I have a full time job that pays around $250-300K a year and I don't plan on leaving it, and this provides enough cash to acquire properties), but rather wealth accumulation -- does it make sense to take the 15 year loan with lower interest so more of the rent payments go towards building equity in the properties?  

The more properties you have the faster wealth accumulates and the faster wealth accumulates the more properties you can buy. 

He had over $500 in accumulated late fees.

Good luck with your thoughts and congrats on the accumulated cash...good problem to have.

Tom,If you don't have $50k - $100K saved up you need to be in the cash accumulation mode.

The cash flow is realized gain every month... the appreciation accumulated is unrealized gain....Unrealized gain is not the same as "fantasy" gain or "smoking" gain as @ Greg.