Thought I'd do a little research into the all-time series between the two. I broke it up into chunks of consecutive games that were played between the two. It does seem as though they really haven't played each other very often when both teams were good. According to sports-reference.com, they've never played each other when both were ranked at the same time.
Head to Head:
1903-04: Nebraska 2-0
1908-09: Nebraska 1-0-1
1913-19: Nebraska 5-2
1930-34: Nebraska 4-1
1937-38: Nebraska 2-0
1940-46: Iowa 4-3
1979-82: Nebraska 3-1
1999-2000: Nebraska 2-0
2011-19: Iowa 6-3
Rankings when not playing (years and number of times each ended the season ranked during that span):
1947-1978: Iowa 4, Nebraska 15
1983-1998: Iowa 9, Nebraska 16
2001-2010: Iowa 5, Nebraska 5
Too bad they couldn't have played more between 1983-98 or 2001-10.
Head to Head:
1903-04: Nebraska 2-0
1908-09: Nebraska 1-0-1
1913-19: Nebraska 5-2
1930-34: Nebraska 4-1
1937-38: Nebraska 2-0
1940-46: Iowa 4-3
1979-82: Nebraska 3-1
1999-2000: Nebraska 2-0
2011-19: Iowa 6-3
Rankings when not playing (years and number of times each ended the season ranked during that span):
1947-1978: Iowa 4, Nebraska 15
1983-1998: Iowa 9, Nebraska 16
2001-2010: Iowa 5, Nebraska 5
Too bad they couldn't have played more between 1983-98 or 2001-10.