A few notes on parallels in Matthew's account of Judas' death

This post is basically a plea for help interpreting this passage:

Then when Judas, his betrayer, saw that Jesus was condemned, he changed his mind and brought back the thirty pieces of silver to the chief priests and the elders, saying, "I have sinned by betraying innocent blood." They said, "What is that to us? See to it yourself." And throwing down the pieces of silver into the temple, he departed, and he went and hanged himself. But the chief priests, taking the pieces of silver, said, "It is not lawful to put them into the treasury, since it is blood money." So they took counsel and bought with them the potter's field as a burial place for strangers. Therefore that field has been called the Field of Blood to this day. Then was fulfilled what had been spoken by the prophet Jeremiah, saying, "And they took the thirty pieces of silver, the price of him on whom a price had been set by some of the sons of Israel, and they gave them for the potter's field, as the Lord directed me."

(Matthew 27:3-10)

1. Jesus and Judas, David and Ahithophel

Jesus is of course the new David, who was betrayed just as David was. Perhaps the worst betrayal for David was of his son Absalom, and of his chief advisor Ahithophel to Absalom's side. Ahithophel's advice is ignored by Absalom in favour of Hushai's, David's mole in Absalom's court, and his response is extreme. He

"saddled his donkey and went off home to his own city. He set his house in order and hanged himself, and he died and was buried in the tomb of his father." (2 Samuel 17:23)

This is must be an intended allusion I think. The parallel is so strong. Any thoughts on its significance? In particular any thoughts on whether it helps us understand the differences between Luke and Matthew's account of Judas' death?

2. The field at Anathoth and the field of blood

Most commentators seem to think that the reference to Jeremiah is a mistake (e.g. Calvin: "The passage itself plainly shows that the name of Jeremiah has been put down by mistake, instead of Zechariah, (11:13) for in Jeremiah we find nothing of this sort, nor any thing that even approaches to it[!]"). However, some point out a possible parallel in Jeremiah 32 but don't really make anything it. I do think Jeremiah 32 is likely to have been in Matthew's mind just as much as Zechariah:

Jeremiah said, "The word of the Lord came to me: Behold, Hanamel the son of Shallum your uncle will come to you and say, 'Buy my field that is at Anathoth, for the right of redemption by purchase is yours.'...

And I bought the field at Anathoth from Hanamel my cousin, and weighed out the money to him, seventeen shekels of silver....For thus says the Lord of hosts, the God of Israel: Houses and fields and vineyards shall again be bought in this land

Zechariah 11 mentions thirty pieces of silver, the potter and the throwing of the silver into the temple. Jeremiah mentions silver and the purchase of a field. However I just can't see what Matthew is trying to say by drawing the parallel with Jeremiah. Jeremiah is a passage filled with hope, as Jeremiah is investing in the land because he trusts God's promises. But the priests buying the field of blood... I don't have a clue. Any help?