When I go back home to visit my parents over Christmas I usually attend a little Anglican parish. For a few Christmases now I have heard a very similar sermon. What makes me uncomfortable with this sermon is the same thing that makes many people uncomfortable with the symbolic interpretation of Scripture, namely, that it is used as an alternative to the historical sense of the text. He begins with the lack of historical evidence in other sources for the story of the slaughter of the innocents and seems to waffle between whether the event simply didn't happen and a more moderate agnosticism about the event. In any case, he proceeds, what the Gospel writer intended to do was make a spiritual point about Jesus' correspondence to Moses, whose birth was also the occasion for the slaughter of innocents. Given that a literary correspondence is what the author meant, we can take this point to heart (that Jesus is the new Moses) without worrying ourselves about the history. It is this kind of move that every critic of Origen ever had in mind.
I think there is a very basic distinction between this kind of spiritualization of the text and a more traditional allegorical interpretation that comes down to who you think the author is. As Peter Harrison has noted in The Bible, Protestantism, and the Rise of Natural Science, the Early Modern period saw a shift away from understanding the things, persons, and events of the natural world as having an intrinsic Christological referent. Harrison argues that with the breakup of Christendom the Reformers had to deny the symbolic nature of creatures in order to forge the Bible into a polemical weapon. For traditionally the words of Scripture were understood to refer to created things that themselves referred to God. Deny that creatures signify, however, and the weight of meaning rests on the Biblical words alone--all the better for air-tight proof-texts. Whether one agrees with Harrison's assignment of causes or not, what one finds in the Early Modern period is an increased emphasis on the human author's intention rather than on God's intention behind the Bible. It is the human author who creates literary figures and allegories. The things, persons, and events that God has authored are not intrinsically figural. But this is precisely the difference between pre-modern and modern exegesis. The only way that moderns can justify to themselves a figural reading of Scripture is if they can prove to themselves that the human author intended it. They never consider whether things themselves might bear the marks of their Author, in which case the created things of nature and history have an importance that they cannot have when the figural is limited to the human author's intentionality. So ironically despite the caricatures, the Patristic method of interpretation ends up granting a higher importance to nature and history (the literal) than much modern exegesis is capable of. If modern biblical exegetes want a spiritual interpretation of Scripture, more often than not it is decoupled from history and is justified by literary considerations of genre (myth, fable, saga, drama, poetry). The question inevitably raised is whose discernment of genre counts?
I am not arguing that the Bible is un-problematically historical (my money is on biblical history being archetypal over against all other history). Just that a hermeneutic of human intentionality doesn't even explain how inner-biblical exegesis works ("latter prophets" interpreting "former prophets," OT interpretation of NT) let alone how the Fathers and their theological heirs did exegesis. In short, us moderns look at the allegory in Origen's eye and do not pay attention to the mythologizing in our own eye.