When the 10th St stadium was torn down in 1981, it was not at all apparent what IU's soccer program was going to become. This was just a few years removed from the athletic department not funding the soccer team's first final four appearance (it was funded through private donations). It would have been ludicrous at the time to spend huge money to renovate the stadium, and would have required a crystal ball of epic proportions. It was pretty impressive that IU built Armstrong Stadium for such a fledgling team (in a sport that was thought to be a fad nationally) and a once a year intramural event. And the cost of Armstrong would have been a tiny fraction of what would have been needed for the 10th street stadium renovation. Plus, this forethought would have also needed to extend back to before the soccer program was a varsity sport at IU, when it was decided not to maintain the stadium, which allowed it to fall into such disrepair. Deferred maintenance can easily increase the cost of repairs 3-4 fold.
I agree with your thoughts concerning Armstrong Stadium. In retrospect It was a great decision. I love the looks of the arboretum in the middle of campus. Besides 10th St. stadium was in poor condition prior to demolition.