Obviously just want to say first that it's terrible that they vandalized his gravesite, I hope they catch and punish whoever did it, and I'll be interested to see if there was any motive.
On to the legend issue: I think at most he's probably a State of Iowa sports legend because I think a lot of people who don't follow sports would have no idea who he was.
Is he a State of Iowa sports legend? I wouldn't say so. To me, in order to be a legend, people need to know who you are. Unless they're an Iowa fan, I don't think a lot of young people know who he is. Christ Street died almost 30 years ago. I'm in my late 20s so I have no memories of him. I remember hearing stories about him at specific times (like when the Iowa player missed the free throw), but before I saw this thread I would not have been able to tell you anything about Chris Street if you had asked me who he was. I don't know that I would have been able to recall that he was an Iowa player. I would have thought you were asking about the gay pride parade in Berlin.
I view Chris Street in a similar way to Pete Taylor. Are they legends for fans of their teams? Yes. Do people above a certain age know who they are and have specific memories of when they passed away? Yes. But I think it's fine to say neither is a State of Iowa sporting legend because there's a sizable segment of sports fans in Iowa who have no idea who they are.