I read about protestants who converted to RC refer to the fact that Luther 'honored" or "venerated" Mary. This "fact" is one of those things that led them to embrace RC. In this respect, these protestants think that they have been "short changed" by their churches.
When I read people say that Luther was a Marian and read the quotes from his sermons and works to prove this, I always ask the question - when did he say this? I do not have to deny that he said what he said, the question is when did he say them, did he say them while he was in RC or were they said after his break with RC? Why should we ask when? Because it matters, a man's understanding goes to development, it goes to maturity and greater understanding. I will naturaly expect him to toe the line before he broke away, that would be expected. The issue is what did he teach after he broke away?
At anyrate, even if Luther praised Mary, the Lutherans do not follow Luther in all things he espoused, the same way that Calvinists or the Reformed do not follow all of Calvin's espoused teachings. Why? Because like any human being their teachings will have to line and be at par with scripture. The issue are the confessions written up by the Lutheran and Reformed Protestants. Luther subjected himself to his fellow reformers and when they drew up their confessions , you will find that there is no veneration of Mary or the saints. In the Apology of Augsburg Confession article XXI, the veneration of Mary and the saints have been rejected and considered a pagan origin.
Lastly for a balanced and well researched discussion of how Mary played in Luther's Christianity see http://www.ntrmin.org/Luthers%20Theology%20of%20Mary.htm#VII