The streetcar is a population circulator -- not a traditional form of mass transit. You'd still have to drive downtown and park somewhere along the streetcar line for it to be of any use to you. And, looking honestly at the line it runs on, unless you want to park in Clifton and take a 30 minute trolley ride downtown, any other place you'd park along the line would probably be within walking distance of the ballpark anyway.
If the issue was about getting people who live downtown to the Banks, maybe there would be a benefit to having the streetcar -- but there aren't enough middle class (read: consumers) residents living downtown to make a streetcar worthwhile.