Is "ir a por" correct?

For years I have condemned the use of a por as a solecism. I have always abhored the sentence voy a por la leche. The rationale was that we should not employ two prepositions together, in this case a and por. But language does not belong to stick-in-the mud old fogies like me, luckily. It belongs to all and has its own directions and rules. So I have changed my mind because there is a reason, I admit, for this a por.
Voy a misa por mi mujer. (Because she wants me to, and to keep her happy.)
Voy a misa a por mi mujer. (To collect her or pick her up.)
He venido por ti. (Because of you.)
He venido a por ti. (To get you.)