Many scenarios already include combat and tactical objectives - the main thing I see in your concept is limiting Exploration dice to 5 unless an objective is completed. That is an interesting thought. Still, heroes are required for Trading, and only heroes always get the Experience benefit from taking others out of action.
I'm not sure how the deck of objectives would interact with many of the extra scenarios, as it seems the objectives would have to be generic enough to apply to most of them, and might take away some flavor from some scenarios. On the other hand, secret objectives are always fun if done right! It might be enough to limit Exploration dice to five normally, and allow scenario-winning warbands the sixth die in addition to an Experience point for the warband's leader.
You might have to try out your concept for a full campaign to see what effect is has on battles and whether it achieves your desired result.