My pleasure! And, I remember when I first encountered the "loop forever" concept in Supreme Commander. It was foreign to me at the time, and I didn't really like the idea. But then after a few days of using it, it clicked. And after a year of playing that game, I couldn't imagine playing a strategy game without that feature, heh. So when I went to build one of my own, that was one of the first things in there.
The more-critical reason for the per-second numbers is actually for things like turrets, though, or other similar temporary constructions. Assuming that your economy has some buffer in it over and above what your docks are consuming (generally the case), you have to decide how quickly you can build up your turrets (or rebuild, as the case may be). Trying to build too many tractors can mysteriously tank your economy, for example, unless you look at their per-second cost and see what's going on.
But, it's definitely useful in a number of contexts. Glad you're enjoying the game!
