I think it would be a nice change to have spy quests also. That way there would be more quests on the list. But, it would also mean people are less likely to battle others instead of just doing quests and epic battles. I don't think the devs would like that. But, as I am not a dev, I do not know for sure. So (in the middle)
The point of attack quests is to pin yourself then be able to spy someone else without worry of immediate hits. With hansels attack quests already bring a major advantage. Spy quests would be pointless for them. Attack builds fight with troops so doing spy quests would mean very little earnt and your spies being open to steals (if you haven't self pinned with troops). It's really not needed, KAW is not a plunder fest to pin on quests for money. No support