Quote: Rather it was the appreciation that Germany lacked the basic social and economic infrastructure
Neither did Gaul but that did not stop them. The Romans, including Tiberius himself in tactical command, campaigned extensively between the Elbe and the Rhine prior to Teutobergerwald. Tiberius probably could be excused for drawing a negative conclusion about the region. For a soldier it probably did not seem worthwhile to push the border forward to another river line when they already had a perfectly serviceable river line in the Rhine. As you say, it would have required a lot of infrastructure development and it should have been obvious to all by that time that the wealth they wanted was in the East, not the dismal north.
All ancient stats are suspect. Some are flat out fucking ridiculous as when the OT claims that 'god' killed 70,000 people to punish David for fucking up a census. The entire population of Judah at the time would have been something under 20,000.
