"How do I know if my spices are still good?"
That's a question I hear a lot and my answer is straightforward: "Smell them."
Instead of being beholden to "best by" dates—which, for the majority of foods, are manufacturers' suggestions—use your nose and sniff. If the cinnamon you bought in 2004 still smells like cinnamon, then you (and your cinnamon) are fine and there's no need to waste money on a new bottle, no matter what the expiration date on the old bottle reads.
I have a half-full bottle of whole cloves that—literally—I bought in the mid 1990s and am still using because the cloves are as pungent as they were almost two decades ago. If the spice companies had their way, I'd be on my seventh bottle by now.
To help dried spices stay vibrant, store them in a cool, dark place. (The freezer is best, if feasible.) Keeping them in a cabinet above the stove or in direct sunlight will force their flavor to fade fast, leading to needless repurchasing.