You buy the mini when it's updated, because you have to assume that if you don't buy, you're nine months away from the next purchasing window.
You have to take the MacBuyer's guide literally. BUY NOW isn't just a friendly suggestion. It's advice designed to save you from this hell. When I see people complaining about updates, I have to ask, "well, why didn't you buy when the iMac was last updated?".
Now I'm not saying this is how Apple should work or that its right. I agree that it is a pain to be caught in mid-product cycle and have no idea whether you're making a good purchase. But this is how Apple works, no amount of complaining will change it, and ultimately you have to learn how to work the system if you want to get the most out of your Apple purchases.
That is the most honest a response about the Apple update cycle I've ever read. That is why the 'if you need it, buy it' credo is unhelpful. There is a good time to buy and a bad time to buy when you're buying an Apple computer. If one simply cannot wait, be aware that you are not getting all that your dollar can buy.