Every upgrade has nice bonuses, but the question is, when is it worth the cost to get them? Smart use of resources is a central tenant of competitive RTS gaming. If you aren't in a position to reap reasonable benefits from an upgrade, don't get it! Herbal Lore is nice to have, but do you want to spend 70 wealth in Classical age for it? More often, you'd be better served investing directly in economy or military. This guide will focus on non-library, non-economic upgrades. Economic upgrades are more straightforward since they payoff the investment directly and immediately.