Okay, so everyone likes to buy gear, mounts, pets, etc. Let's look at this as revenue out.
We all like to make gold, too (why you're here, reading this blog). Let's look at this as revenue in.
So, if revenue in is greater than revenue out, we have profit. Profit is good. If revenue out is more than revenue in, this is called a loss. Loss is bad. I know this is a "duh" thing, but raiders still stand in the fire, PvPers still fight on the roads (as opposed to on the flag, I'm sure we've all seen/been that armchair General who announces it), and we still have WoWBankers who are less than gold-capped.
I'm not saying that you need to have a static 214k on you at all times, I'm saying that just because you know how to MAKE gold, doesn't mean you know how to be WoW wealthy. How do the rich stay rich? By not going out every night and blowing $5,000 on booze and drugs. Or buying a new $4,000 TV every day, whatever.
A good add-on program I used was Gold_FuBar. I'm usually not an add-on guy (anymore, at least), but this was one of my favorites. It showed me gold coming in, gold going out, and helped me find out if my investments were profitable. It could show me all the gold I have to my name, on all my characters, and it would even track what I spend and make.
Another helpful add-on to keep track of what you have is the Beancounter tab on Auctioneer. To be honest, I'm not as huge into min/maxing my gold output as I could be. When cutting rare gems, I put them on the AH for the lowest price (they're 100% profit for me, usually, after I sell the uncommon quality gems). When they inevitably come back to my mailbox, I re-list. If I see them coming back 10-12 days in a row, I know it's not a good gem to continue cutting; I'll usually reduce my # cut to 1, and then eliminate if it's still not selling (and I'm not being undercut). But I digress; you can use the Beancounter tab to see what you've sold, what you've bought, and what you've put on the Auction House that hasn't sold. You can use this data to analyze what is selling and what you're spending too much on listing fees for.
Let's say you bought 10 stacks of elementium ore for 90g, but then 5 days later you say, "Hmm, I wonder what I bought those for." Just open up your handy-dandy Beancounter tab, and you can find out immediately. You can also find what you sold by looking at the raw materials, and then either do the math to see if you made a profit, or just mouse-over the Fu_Gold tab to see if your net gain was positive. Handy!
-Making gold doesn't mean you're rich
-Fu_Gold and Beancounter can help track how much you've made and spent.