Which term is associated with a lack of moderation or balance in one's interests?

The term that best represents a lack of moderation or balance in one's interests is "excess." This term conveys the idea of going beyond limits in various aspects of life, whether it be in behavior, emotions, or interests. Excess implies an overabundance or extreme degree in something, which makes it difficult to maintain balance.

While egomania refers to an excessive preoccupation with oneself, which can certainly indicate an imbalance, it is more specifically focused on self-centeredness than on broader interests. Obsession denotes a persistent and troubling fixation on a particular thought or activity, which also indicates a lack of balance, but it is typically associated with negative consequences and intense emotional distress rather than just excessive behavior. Fervor suggests intense and passionate enthusiasm, which may not necessarily imply an absence of moderation.

Thus, excess is the most suitable term for describing an overarching concept of imbalance across a wide range of interests.