Lets use 9 for the sake of math. I'd say Iowa typically wins 2/3 of the recruiting battles with ISU, honestly, probably more. So on a given year, Iowa is probably bringing in 6 or the top 9 guys. That number seems pretty close, 2016 was 6, 2015 was 5. Occasionally, there will be a guy that goes out of state to Michigan, Neb, Miami, etc, but that would affect ISU too.
So Iowa is probably going to have 24 or so players from the state of Iowa on a roster of 85 (28%). Way more when you look at walk-ons that earn scholarships and so on, probably closer to 35% on average. If ISU starts being successful in football and Iowa's success stays similar or goes down, you can bet that over time that 2/3 will get closer to 1/2, possibly worse. All of a sudden that 28-35% of the roster experiences a pretty major downturn in quality as more high school players would consider ISU an viable alternative.
ISU being good has an impact on Iowa, and it isn't a good one.