Dow 10,000? Slam dunk. Dow 11,000? Not so much.

Here's an oldie but a goodie: Dow 10,000.

We last saw that level (on the way up, that is) six years ago, and we first crossed Dow 10,000 a full 10 years ago. (The latter fact is no doubt deeply depressing to buy-and-hold investors, but at least it has a nice symmetry to it.)

So here we are oh-so-close to regaining the psychologically significant Dow 10K, and yet in so many ways, it feels too good to be true. You needn't be a full-on bear to figure that this current rally is getting a little long in the tooth. The Dow's up 50 percent from the March bottom, the broader S&P 500 has gained nearly 60 percent since that time and the tech-heavy Nasdaq Composite has engorged itself by nearly 70 percent.