St. Louis has some great museums, but I don't think any of them are considered world class, with the exception maybe of the Zoo. That part of downtown is just a dump, so anything we do to it will be an improvement.
If I lived in the county or in the city of STL, I'd be calling my political reps daily to protest spending that kind of tax payer dollars on another sports arena. But them I'm not a football fan, so I could really give a rip about keeping our current team or getting another one here. Why does the city need to spend that kind of money for us to watch 8 football games?
Now, I am a big soccer fan, so I wouldn't be opposed to a stadium built for an MLS expansion team. It's not as many games as a baseball or hockey season, but it's still more than double what an NFL team plays at home. Not to mention that there are teams from other countries and leagues that could/would play here. I went to the Chelsea/Manchester City game a couple years ago at Busch Stadium. It sold out in about 15 minutes. I think there's an appetite for professional soccer in STL.
The last I heard about the new football stadium was a proposal to spend upwards of $900 million. The proposal for the Jacksonville aquarium was $85 mil plus $15 mil for startup and inhabitants. Seems to me that an aquarium would be a more useful use of that kind of money. Hmmm...spent 1/10 of the money for a stadium on something else that attracts people and revenue to the city? Sounds like a better strategy to me.