While there still is much discussion regarding Luther and how he saw Mary, there is no question that he did hold her in high esteem, and retained the feasts and festivals of Mary that were supported by Scripture. Luther never stopped studying; the theology of Martin Luther at the time of the posting of the 95 Theses evolved greatly over time and coalesced along with other Lutheran theologians into that reflected in the unaltered 1580 edition of the Book of Concord.
BTW, he was buried with his rosary, and at one time wrote that only those with strong faith should use the Rosary as those of weaker faith might be lead to superstition. He did not prohibit or personally reject its use.
In LCC/LCMS our Calendar retains the following feast days: St. Mary, Mother of our Lord (Assumption/Dormation); Annunciation; Visitation; Purification and maybe a few more. Many Lutheran Churches use blue paraments and vestments for Advent season, blue is the colour associated with the Blessed Virgin.
Martin Luther composed this to use at the end of the Daily office as a substitute for some of the less biblical Marion hymns and prayers:
Luther's 'Evangelical Praise of the Mother of God'
O Blessed Virgin, Mother of God, what great comfort God has shown us in you, by so graciously regarding your unworthiness and low estate. This encourages us to believe that henceforth He will not despise us poor and lowly ones, but graciously regard us also, according to your example.
A good article can be found here:
by Deac. Betsy Karkan It’s probably not what you think. In his devotional writings on the Magnificat, Luther carefully outlines how we should and should not honor this “Most Blessed Virgin Mother.” Luther neither wants to give her false attributes or idolatrous devotion, nor does he want to...
lutheranreformation.org
In our Liturgy for the Daily Office - Vespers, we sing the Magnificat (there are actually multiple settings of this hymn in Lutheran Service Book; one of the oldest Christian Hymns and is found in the first chapter of St. Luke's Gospel:
My soul magnifies the Lord,
and my spirit rejoices in God, my Savior;
For He has regarded
the lowliness of His handmaiden.
For behold, from this day
all generations will call me blessed.
For the Mighty One has done great things to me,
and holy is His name;
And His mercy is on those who fear Him
from generation to generation.
He has shown strength with his arm;
He has scattered the proud in the imagination of their hearts.
He has cast down the mighty from their thrones
and has exalted the lowly.
He has filled the hungry with good things,
and the rich He has sent empty away.
He has helped his servant Israel in remembrance of his mercy
as He spoke to our fathers, to Abraham and to his seed forever.
Here are a couple settings:
From the Book of Concord:
On account of this personal union and communion of the natures, Mary, the most blessed Virgin, bore not a mere man, but, as the angel [Gabriel] testifies, such a man as is truly the Son of the most high God, who showed His divine majesty even in His mother's womb, inasmuch as He was born of a virgin, with her virginity inviolate. Therefore she is truly the mother of God, and nevertheless remained a virgin. ~Solid Declaration VIII:24
Semper Virgo!