Ask GP as he has been to every ballpark in North America.
As for that kind of road trip, where your visiting Detroit, Cleveland or Pittsburgh, I don't think you have to spend more than 1 night in Detroit or Cleveland (if any at all). Pittsburgh is actually very nice from what I've heard and they have really done a good job at cleaning up their city image in comparison to 5 to 10 years ago.
I really don't have any desire to visit Detroit or Cleveland unless its for a baseball game and I'd only go for the day. Both cities are dives. Around the ballpark in Detroit is nice with some good restaurants and bars, but I wouldn't go walking around the city like you would here in Toronto especially at night. Just use your street smarts and that applies to anywhere you go, and you'll be fine.
You should do a road trip on the west coast if you haven't already, which is far better. Start down in San Diego, then hit up Anaheim, Dodgers Stadium, San Fran, and maybe even Seattle. Only difference is that you'll have to pay for the flight there, but you could get good deals like a month or two in advance for around $500 for a RT to Cali.