As far as seeing Detroit:
There are techno bike tours here: http://www.wheelhousedetroit.com/tou...aspx?tourid=32
If you are awake on Saturday going to the Eastern Market is always good people watching. http://www.detroiteasternmarket.com/ Farm fresh fruit, homemade goods, stores, restaurants, artists galleries. Best pizza joint in the city is Suppinos right on the side of the market. Nice graffiti around there too. Plus bonus points if you see others walking around with a Movement wrist band! In fact this would be the most "authentic Detroit" experience.
Russell Industrial Center is a huge artists community. They have a bazaar open but I have heard the merch available isn't the best (thinks socks, belts and used CD/DVD's). But some of the artists there have their studios open to check out stuff. Haven't done this myself but there are legitimate galleries there. http://ricdetroit.org/2010/?id=home
Guardian building lobby is a sight to behold. It's right downtown. Couple clothing stores and coffee shops in there as well.
Heidelberg would be a short cab away from the city but is always pretty cool. http://www.heidelberg.org/
Just walking around the midtown area (where old miami is) is neat. It's thriving again. A few stores, restaurants, wayne state university, DIA, Historical museum, artist galleries are all in this area. http://detroitmidtown.com/05/directory.php?msub=6
For the good Christians out there there are many architecturally fascinating churches in the downtown and surrounding areas. Sweetest Heart of Mary, Old St. Mary's, SS peter and paul jesuit, holy trinity etc. etc. Google those names or historic detroit churches and you could spend a day checking them out!
As far as seeing the abandoned buildings:
I don't do it but it is done quite often. Do be careful and it is not recommended. Some moron, and it happens about once a month, had to get rescued from falling down a few flights of stairs in the train station last week. Plus in most of the buildings illegal scrapping is going on and you don't want to get caught up with those people. Also most of the buildings in and around downtown are either being rehabbed, have been torn down, or are better secured lately. (Places I have heard lately require ladders to get in and dodging security guards.) You have to go some of the outlying warehouse areas and most of those buildings aren't all that significant really and are more dangerous and loaded with scrappers. If you want to go back home saying you walked around an abandoned building in Detroit go ahead and give it a shot I guess, but it could be a quick way to end your weekend.
Restaurants that I can recommend:
Downtown: Detroit Beer Co., Suppinos, Mudgies Deli, Russel St. Deli, Bucharest Grill, Slows BBQ, Small Plates (if you want a nice night out), American or Lafayette coney islands, Grand Trunk Pub (A.K.A. Foran's-they'll have technos throughout the weekend with awesome Michigan microbrews!!!), above Grand Trunk Pub is Motor City wine for the vino lovers out there and they are also techno music friendly, Jacoby's for good beer. Any of the bars downtown will always have a decent burger available otherwise google the rest of the places for locations and hours.
Midtown: Honest John's Bar, Union Street, Avalon Bread Co., Cass Cafe, Byblos, Slows BBQ to go (much quicker than the sit down restaurant) Motor City Brew Works (they supply the beer for Need I Say More), Traffic Jam and Snug. There are a bunch more places near the university that I am not sure will be open because the students won't be there.
Have fun! As with any city travel in a group, don't look or act like a moron.