I spent close to 5 years living in Washington DC and used the subway system there extensively. It was a wonderful convenience and I genuinely wish we had something like that in Cincinnati. I voted for the regional light rail plan back in 2002 and I'd love to see the idea revisited in the near future.
However, the streetcar isn't rail transit. It's a 15-20 block / 2-mile loop that connects several downtown "attractions" that are already within walking distance of one another. You still need to drive downtown (paying for gas and parking) to use it. If you already live downtown, you can just as easily walk everywhere it takes you in roughly the same amount of time it would take to wait for a car, pay the fare, board, and ride. I've worked downtown for 6 years now, and I've yet to hear someone complain that downtown is too hard to get around. Fountain square is a 5-10 minute walk from the stadium, OTR another 5 on top of that.
Like I said, I give the Mayor credit for fighting for years to make his vision a reality -- but I can't see this as anything other than a giant waste of money.