I believe Alexander III gave Miechen a good dressing-down when he heard she had been feeding information to Bismark, no?
She certainly had access to state secrets - she was sleeping with the man who was number two in the empire!
While Dagmar certainly did all she could for Danish firms and businesses in Russia, there is no denying that, I do not think that she was responsible for the move away from Germany. It was Alexander II alone who followed a pro-Prussian foreign policy (which brought Russia nothing, by the way!) - everyone else was against it, including the Empress (a Hessian princess) and the heir himself, the future Alexander III. During the Franco-Prussian War, everyone was aghast when Alexander II seemed so pleased at the Prussian victories. But the move away from Germany towards France was very much the fault of Prussia herself - and it was Alexander III who made all the decisions. Yes, Dagmar was incredibly anti-Prussian, but at that stage she did not dare to try and influence her husband. If Alexander III had been pro-German, she could certainly not have been able to make him change his mind! Alexander III was a very astute tsar - he took capital from everyone to build up Russian industry, and kept Russia out of wars. If anything, it was Kaiser Willie and all his games and intrigues that turned Alexander III (and Edward VII) against him, far more than any influence from their wives.
I do agree, of course, that Miechen was a strong woman and a notable host. It sometimes happens that the most unpleasant people make the best politicians and rulers!
I wonder what feelings Miechen secretly harboured about being empress herself? After Nixa died, Alexander only wanted to marry "Dusenka" Mescherskaya and had to be forced by his father to go to Copenhagen and propose to Dagmar. Ideally, he would have been allowed to make a morganatic marriage to Mescherskaya and the throne would have passed to Vladimir and Miechen..... Both would have loved that, I feel.... Funny how close they also came in the next generation, with Kirill and Ducky.... To be honest, I have never understand why Miechen kept her Lutheranism for so long. Was she so religious? All other German princesses dropped it like a hot cake, even Alix, if it meant marrying a tsar or a grand duke!