Well, you must be using a different Bible then mine. This is what my King James Version says....
Luke 1:28 And the angel came in unto her, and said, Hail, [thou that art] highly favoured, the Lord [is] with thee: blessed [art] thou among women.
Click Here for a more thorough break down.
You'll notice that the Greek word for highly favoured is charitoo which simply means
1) to make graceful
a) charming, lovely, agreeable
2) to peruse with grace, compass with favour
3) to honour with blessings
I accept that Mary was blessed but so were many other people in the Bible.
Genesis 1:28 God blessed Adam and Eve.
Genesis 9:1 God blessed Noah and his sons.
Genesis 24:1 God blessed Abraham.
Genesis 25:11 God blessed Issac.
are just a few examples. Just because these people were blessed of God, that doesn't translate into receiving our prayers, interceding for us, or even being without sin.
What I find most telling is in the very same book that you claim gives Mary special honour and blessings, Jesus corrects a 'certain woman' for trying to do the same as you.
Luke 11:27,28 ¶ And it came to pass, as he spake these things, a certain woman of the company lifted up her voice, and said unto him, Blessed [is] the womb that bare thee, and the paps which thou hast sucked.
But he said, Yea rather, blessed [are] they that hear the word of God, and keep it.
Another incident reveals that that Jesus didn't elevate Mary over anyone else who does the will of God.
Matthew 12:47-50 Then one said unto him, Behold, thy mother and thy brethren stand without, desiring to speak with thee.
But he answered and said unto him that told him, Who is my mother? and who are my brethren?
And he stretched forth his hand toward his disciples, and said, Behold my mother and my brethren!
For whosoever shall do the will of my Father which is in heaven, the same is my brother, and sister, and mother.
I think the word that Luke used is " kecharitomene " and I don't think it is used anywhere else.
But it raises the question of how much importance do we give to a translation. The KJB is a great piece of literature, but it was dependent on its sources, and , of course, on the word choices of its translators. So it reads as you say, just as Jerome said "gratia plenus." Inevitably one's theology influences the words we use.