Q. Is vanilla extract with a date of 1974 too old to use? What about the shelf-life of other spices and powders?
Haven't been doing a whole lot of baking, have we? Yes,
has at least 35% alcohol, but that doesn't mean that it improves with age like fine wines. The folks at Nielsen-Massey Vanillas (whose goal, admittedly, is to sell more and more vanilla) say you can keep properly stored vanilla extract for four or five years. Proper storage, they add, implies a tight seal and room temperature.
Vanilla is expensive, but we think you can splurge more than once every 28 years, indeed, more than every 10 years. Buy a smaller bottle, if you must. And who knows, having a half-filled bottle of vanilla on your shelf that's only four or five years old may inspire you to bake a little more often.
In answer to the second part of your question, read The Shelf-Life of Spices.