Alan-
Your "rule of thumb" (use other people's money when you can) IS sometimes good business- if the money is cheap enough, and the ROI is high enough. However, it's also like playing with a loaded gun- bad stuff can happen pretty quickly if you aren't very, very careful. There's a time an place to borrow money, but the less you can do it (and retain enough liquidity), the better off you'll be in the long run. Having an open line of credit and using it are two completely different things.
Additionally, I still contend that buying a plastic toy car has nothing to do with business (for most of us)- it's consumption, pure and simple. Business produces revenue and income, and it takes a certain amount of capitol to keep the wheels turning. Borrowing money for stuff we don't need and will depreciate is paying twice for the pleasure.
I still say: if you can't afford the stuff you want now, either wait or curb your expectations.