The light of the East
In light of my new, contradictory approach, I suppose I should preface this by saying that deeper thought about Monteverdi, the Vespro, and the Counter-Reformation convinced me that they are neither a liturgical exercise per se nor Orfeo in St. Mark's. Parrott's recording is lovely, and it is certainly a good one to enjoy; however, I don't think that it represents the musical milieu (such as I understand it) of the time.
East of Indiana, anyway. In the last twenty or thirty years, along with a lot of Baroque stuff, Monteverdi's 1610 Vespro della Beata Virgine has become incredibly influential and popular. There are many very good recordings out there, mostly on period instruments, but there are two (really, two schools) that dominate. John Eliot Gardiner's Archiv set and Andrew Parrott's EMI/Virgin set. Gardiner seems to take the view that (1) Monteverdi, in a substantial way, prefigures Bach and (2) the Vespro are - essentially - a dramatic cantata with a little plainchant thrown in for flavor. His earlier performance, based on a limited audition, sort of reinforces that opinion. Parrott, on the other hand, takes Monteverdi at his word and creates a solidly liturgical record. It is not a stretch to imagine vespers in St. Mark's, one evening in the early 17th century, sounding precisely as Parrott directed these.
I prefer Parrott's sober, liturgical performance. The chamber scale and intense soloist involvement, especially in choral motets, really recreates the sort of performance that Monteverdi would have imagined and heard. Gardiner II is the sort of performance that uses drama, intense orchestration, and polyphonic density to emphasize what is to come. Parrott uses Monteverdi's score to link back to the past. There are deeply conservative elements, for all the innovation, in the Vespro. Gardiner chooses to ignore them, and that makes for grand entertainment.
Sometimes, though, less is more.