On the other hand, I think a lot of intelligent people overestimate the value of intelligence (in a vacuum). And problematically, the concept of superintelligence seems to have been defined by these very people, so we can't really have a reasonable conversation about what greater-than-human intelligence would really look like or be capable of.

What vacuum? do you really still think it can be contained? It already escaped on accident. What more do you need? If you're argument is well it escaped X, but it hasn't escaped Y yet then you should take the first escape as sign as to where it will escape next. Don't keep claiming something can't happen because it hasn't happened before. Unless there's some law of physics that prevents it then escape is possible.