Are there any commentators (I couldn't find one) that support the idea that those in the house thought it was Peter's spirit that was at the door and not just a run of the mill guardian angel?
N. T. Wright endorses this view. He says: "The praying Christians ... believed that Peter must have been executed in the prison. They, like most societies ancient and modern, knew well enough that grieving friends and relatives sometimes receive what seems like a personal visit, vision or apparition in which the recently deceased appears for a few moments, perhaps says something, and then disappears again" (p. 134), and the expression "his angel" refers "to the intermediate 'angelic' state in which the person will now remain, with his body dead and buried" (ibid). I think D. A. Carson has a similar view.
As I went into my post above, there is evidence both for and against this view. The main difficulty with the guardian angel explanation is that the "angel" resembled Peter in voice. There is however a rabbinical, tho late, tradition claiming resemblance between guardian angels and the people they protect: "It was Esau's angelic prince with whom Jacob struggled: to this it was said, 'I have seen your face as the appearance of the face of the angel, as the angel's face was, so is your face' " (Genesis Rabba 78, [50a]). But this may not be sufficient to resolve the difficulty. The account in Acts 12 is also paralleled in the story of Jesus' arrest/execution/resurrection in Luke, and in the paralleled text, it is Jesus who is misapprehended as a spirit or apparition. This would support the interpretation that Rhoda's housemates referred to Peter's postmortem spiritual state.
Those in the resurrection were frequently described as like angels, or having angelic splendor, or joining in fellowship with the angels, and texts that do not presume a future resurrection may indeed describe the dead as having such a state, and other texts may presume that the intermediate existence occurs in heaven:
"And I know that there is hope for him whom you have created from the dust for the eternal assembly, and the perverse spirit you have cleansed from great transgression to be stationed with the host of the holy ones and to enter into fellowship with the congregation of the children of heaven. And you have apportioned to man an eternal destiny with the spirits of knowledge" (1QH 3:21-22).
"Formerly you were worn out by evils and tribulations, but now you will shine like the luminaries of heaven; you will shine and appear, and the portals of heaven will be opened to you...for you will have great joy like the angels of heaven" (1 Enoch 104:2-4).
"And there I saw another vision, the dwellings of the holy ones, and the resting places of the righteous. There my eyes saw their dwellings with his righteous angels and their resting places with the holy ones" (1 Enoch 39:4-5).
"At the resurrection people will neither marry nor be given in marriage; they will be like the angels in heaven" (Matthew 22:30).
"People depart from this life in accordance with nature's law, thus repaying what God had lent them...Their souls remain without blemish, and obedient, and receive the most holy place in heaven. From there, when the ages come round again, they come back again to live instead in holy bodies" (Josephus, Jewish War, 3.374).
"When they, therefore, will see that those over whom they are exalted now will then be more exalted and glorified than they, then both these and those will be changed, into the splendor of angels and those into startling visions and horrible shapes...For they will live in the heights of that world and they will be like the angels and be equal to the stars. And they will be changed into any shape which they wished, from beauty to loveliness, and from light to the splendor of glory...And the excellence of the righteous will then be greater than that of the angels" (2 Baruch 51:2, 10-12).
"Blessed are they that possess their wives as though they had them not, for they shall inherit God. Blessed are they that have the fear of God, for they shall become angels of God" (Acts of Paul 3:5).
"Fill my heart with good things, Lord, as an earthly angel, as having become immortal, as having received the gift which is from you" (Prayer of Jacob, 19).
Guardian angels of individuals are mentioned (or thought to be referred to) in such texts as Psalm 91:11-12, Jubilees 35:17, Philo, Gig. 9; Testament of Levi 5:3, Pseudo-Philo 11:12, 15:5, 59:4, Matthew 18:10, Hebrews 1:14, 3 Baruch 12-13; t. Shab. 17:2-3, Sifre Num. 40.1.5.
Some other interesting things about this verse....Much of Acts is allusive of Homer and it has been suggested that ch. 12 parallels the story of Priam's escape from Achilles (with the help of the god Hermes) and his appearance to Cassandra (cf. Iliad, 24)....The verb mainó "to be mad" also occurs in Acts 26:24 with reference to Paul's belief in the resurrection...and the Codex Bezae has somewhat different wording in Acts 12:15 (elegon pros autén tukhon ho angelos).
