N7 Missions are not quite as extensive as some of the optional story missions offered throughout the game, but they do provide additional means to strengthen your squad through experience earned for accomplishing these objectives and the variety of weapon and armor mods you can acquire during these sorties.
Additionally, several Citadel side quests can only be started or completed by hitting these locations and lifting key items from them. You can also acquire improved Was Assets by finishing these missions.
N7 Missions can also serve as a Primer for Mass Effect 3 multiplayer, as every mission takes place in a map that is also used for the cooperative battles.