I don't think Vatican II has as much to do with those declining numbers as other factors; of course, I feel that John XXIII was probably one of the three or four greatest Popes of all time, and I'm not Catholic, but that's what I think.
VII - virtually "protestanised" the Church.
Take it the other way, if the Church hadn't modernised, and the priests were still the mysterious "intermediary" - would the numbers be any better?
My father was an altar-boy and a good catholic boy, learning latin and all.... but stopped once VII happened... if he couldn't use the latin. What's the point?
I have no problem with a number of the edicts of Vatican II, however I would argue that Vatican II has clearly established a new culture in the Church that has been detrimental in many way.
I think you're too quickly disposing of the argument other factors, wholly separate from Vatican II are the cause of the church's statistical downfall.
Just a few examples which may or not actually be pertinent
1) The ban against cleric marriage-might be responsible for the lower levels of modern clergy
2) Changes in modern culture beginning right around the time of Vatican 2, the late 60s were an exciting era that might have changed American views of organized religion (let alone Catholicism) irrespective of what the church did to change itself
3) Modern lifestyle where often both parents work, or where the modern work week isn't really a 9 to 5, monday through friday week--if it ever was to begin with, preventing church attendance...
etc...I think you really need to consider factors like that before saying it was Vatican II