I think the CU rivalry is a good backdrop for this conversation. We did not consider the Buffs a rival when they considered us a rival. That took years, and that's despite a long history of playing every year. That's not snobbery, it's just that playing Colorado was no different than playing Kansas. Suddenly they just decided it was THE rivalry, and we weren't having it.
It became our main rivalry after 1) they won a national championship, 2) they beat us a bunch, 3) the Big XII ended our yearly game with Oklahoma, and 4) when we reciprocated the feeling.
You know it's a rivalry when, after not playing for long enough that two recruiting cycles have passed, both teams' fans still wanted to win this year's game with a passion.
Most Nebraska fans don't currently feel that way about Iowa. For them, it's about Colorado around 1989-level hate toward Iowa. CU had already declared we were their rivals, we didn't feel it, but we wanted to beat them every year. And we hated them.
We just have to wait and let this thing with Iowa percolate. I think it will definitely get to where every Husker fan thinks it's a rivalry.