First let me say that I live next to Comerica park...
Secondly, don't listen to anyone who tells you to walk to or from any of the big venues from the Motor City Casino. The casino has limo's and cars and shuttles for it's guests that run all night and are free. They will pick up any of their guests anyplace in the greater area free, all the casino's offer this service. I don't advise anybody to walk back to the motor city casino late at night from the Grand Circus park area, especially if you're not familiar with that area of the D. Once you leave woodward on the north side of 375, you're taking a risk until you reach the safety of the casino. The Detroit Police canvas the area around the ballpark pre and post game, but after a while after the fun is over, you're on your own.
Of the 3 casino's, MGM is the nicer of the 3. It's walking distance to Comerica, but not the Joe, but alas the casino will take you anyplace and pick you up if you're a guest.
If I had to stay at a hotel in the D to enjoy the trip you describe, I'd go with the Atheneum on Brush in greektown or the Marriott at the RenCen. The Atheneum is definitely walking distance to both the Tigers and the Wings, they offer shuttle service as well. The Marriott for the view and service. There's a people mover stop at both of those hotels. There is a Joe Louis ppl mover stop and a grand circus ppl mover stop for Comerica. It runs late and it's only $.75. The security on the People Mover is outstanding. I have witnessed those police respond very quickly.
Things to do? You're already doing the 2 best things to do in Detroit in Sept., the Tigers and the Wings. The pre/post game spots for your first trip to the D? The wings is easy, pre/post game at the hockeytown Café - A MUST for a wing fan, it's on Woodward, any cab driver will have you there in 2mins. Another Detroiter spot for Wings Pre/Post games is Cobo Joes. It's right outside the arena on Congress, it's a Wings fan Mecca...
Tigers pre/post game fun you have many more options. Right outside the ballpark are some great restaurants. Chelioses is right there. Rub,Taqo, Angelina's, The Elwood are all right outside the ballpark plus many others.
I will tell you what I tell my friends from around the D when they ask me where to go for a kickass dinner in the D. I tell them Slows BBQ in Corktown, the food is awesome(plenty of shuttles to and from this area to all the sporting events from this area, best bbq in Detroit. Ottova Via, the best Italian in the D, not far from Slows in Corktown. The menu and winelist at Ottova Via are pretty great. You will thank me as have other friends after sending them there...