It kind of depends on where you’re coming from. From your track record I’m guessing that you live somewhere in Ohio. If that is the case, then SFStL would be rather far out of your way.
But, anyway… the park is worth a trip if you have the time. Crowds usually aren’t too bad on Sundays and the weekend ride op crews usually do a pretty good job of keeping lines moving. SFStL never has signs that tell you wait times, but in my experience: Boss full queue – 45-60min.; Mr. Freeze from where you enter the building – 30min.
SFStL has more than 15 rides, but the 6 coasters are the big draws – the flat ride selection is pretty weak. I would advise riding B:TR at StL even though there is a clone in Chicago – the one in StL is the mirror image (namtaB) and the lines for it in Chicago get pretty long.
Don’t pay for the preferred parking – it is a rip off.
Have a good trip.
Kip