I find the contention that the author of Isaiah 7 was referring to events of their own time to be entirely convincing. My starting point with any text is that it is written for the author's own time, unless there is reason to think otherwise. I find nothing in Isaiah 7 to make me think otherwise. I think Collins' discussion of the possible identity of the young woman or the child misses the point. (219) To me, 7:14-15 relate solely to the timing within which all of the subsequent "on that day" statements will occur.
When I read 7:14-15, I don't see Isaiah predicting that some young woman somewhere will have a male child and give that child the name Immanuel. Instead, I see Isaiah as crafting an argument that a child who is to be born relatively soon (from a woman who is already "with child") will be eating curds and honey (because of an excess of food due to the desertion of the land) before the child reaches the age of reason. The name Immanuel is symbolic of God's continuing presence in the house of David.
Should this interpretation give Christians agita because it runs counter to the interpretation that leads to the doctrine of the virginal birth of Christ? For me, no -- the idea that God could take a prophecy that was meant for a particular age and make it equally applicable in another age is entirely consistent with the way God acts in my life. Likewise, the idea that God could take a dubious translation of 7:14 and make it a part of God's incarnation is no more surprising to me than God raising up sinful and broken people (such as myself) to proclaim God's word and to do God's work. I believe that we can try to determine what a text meant in its original context without denying the meaning of the text in our own context.