Just picked up on this thread, and I thought I´d just add a few thoughts, because (a) I work a lot with herbs and spices and (b) it´s important to distinguish between "spices", "spice mixes", and "herbs".
You can look for a definition of "spice" in the web, and simply get confused, but I think in principle, it´s a seed, dried flower, bark, seed pod, etc. used to condiment food. A spice is also potent in flavour, so needs to be used with caution.
A herb is usually the leafy part of a green plant, again used to flavour food. Did you know that the largest "Herb" plant in the world is the banana tree?? Ok - let´s forget that bit.
Herbs can
generally be used more abundantly than spices ( think tabboulé, mint sauce,Indian mint/cilantro mixes,chimichurri or pesto), but that doesn´t mean some of them are not "potent" as well.
A spice mix, which is a combination of a number of different spices, could be something typical of a national cuisine ( garam masala, Chinese 5-spice, panch puran, ras-el-hanout, etc) or could be a commercial blend (Mexican Chile powder, curry powder, Creole seasoning, Old Bay seasoning, etc.), which is generally sold in a jar!
In my humble opinion, the best way to enjoy the full flavour of spices is to buy
whole spices and keep them in a cool, dark place. I´ve got a fridge especially for them. If you buy ready ground spices, you´ve got two problems. 1) you don´t necessarily know when they were ground. 2) When you grind spices, the flavour will disappear within 4-6 months. With herbs, they´re far better fresh, although I´ve always got some dried ones just in case.
Not everyone, however, has the luxury that I do of being able to work from home 95% of the time - which is why I grind all my spices when I´m making a dish (thanks to my wonderful spice grinder and original molcajete).