1) While being too specific will limit their utility, Qualities can not be too broad, either. Avoiding too much specificity is the concern of the player, policing the breadth of Qualities is the province of the referee. Generally speaking, the broader the Quality, the less it should be allowed to apply to specific situations.
Example: A character has the Quality "Dexterity +1". He enters a chamber split by a bottomless chasm, crossed by a narrow plank. On the other side he spies a chest. Deciding to try the plank, he must make a roll of 9+. Since this involves a general sense of balance, the referee allows the Dexterity Quality to apply. Once safely across, the player announces his character will pick the lock on the chest, and petitions for the application of his Dexterity Quality. The referee would be right to deny the bonus. The player is attempting to use a broadly defined Quality for a very specific task. In this instance a Quality of Thievery would be much better suited, and still broad enough to enjoy multiple uses.
2) Qualities which directly affect either combat or spell casting must be specific, on the other hand. A warrior with the Quality "Strength of Ten Men" would be able to use the bonus on weight lifting, breaking down doors, perhaps arm wrestling, but not as a damage bonus, under any circumstances. That would require a Quality limited to providing a bonus in combat situations, and nothing more. Likewise, a general Quality of "Smart as a Whip" will not affect spell memorization, use, or acquisition. Those activities would require Qualities unique and specific to them.
Generally speaking, a single Quality that can be used in so many ways that it is used almost every turn, is too broad and needs to be reined in. A Quality that only sees use once every session or two may be too specific and should be rethought.