I see why you would want this option, but it brings up another balance issue: having more eyes-in-the-sky for a team than usual. If spectators were allowed to look freely around the map (fog of war or not) they would be able to catch incoming ganks and watch hotspots while the players could focus on laning.
Even if spectators were locked to champions, they could watch the minimap and give warnings.
Ideally, for your suggestion, spectators would be locked to players, completely unable to move the camera, and the minimap would be disabled. You could still help with builds and give advice for teamfights but it would be more like having a coach and less like having a lookout.