IMHO, blessed Saint Augustine was wrong on this (as a Protestant, I also disagree with Augustine's Pro-Papal Ecclesiology -- although I am of course a great fan of his Predestinarian Soteriology). At the risk of psychoanalyzing a far better man than myself, with no professional psychological credentials, and across 1600 years of elapsed time -- it's worth remembering that Augustine may have had a few minor sexual hang-ups, resulting from his debauched youth (and his admirable renunciation of debauchery after his Conversion).
The first Couple, by devoting all their efforts to "Serving God", has acheived a 100% "return on their investment" for the benefit of Christ's Church. Well done, thou good and faithful servants; enter now into the Joy of thy Lord.
But the second Couple, by raising up Children for Our Lord, has acheived a 250% "return on their investment" for the benefit of Christ's Church (perhaps compounded, generation upon generation, as they serve as Christian Patriarchs to their grand-children in their golden years).
Which Servant has accomplished more, for the Kingdom, with the Talents which God has given them?
Augustine was taking the Short View of things (which is a bit ironic, given his endorsement of "Long-View" Amillennialism). I think it is probably better, particularly for the Amillenialist (unless I am mistaken, orthodox Lutherans are confessionally Amillennialist) to take the Long View of things.
Best, OP
You are correct about confessional Lutherans being Amillennialist. I guess I was trying to make the point that some of the views on marriage and sex have changed through the ages, and held up Augustine (a personal favorite of mine) as an example of one who viewed marriage as a concession to the sinful nature of man and not as a holy vocation.