Hello! I don't know of any railroad festivals of events but as someone living in downtown Detroit I can say there is plenty of train action going on. Downtown and the surrounding areas you can see Norfolk Southern, CSX, Conrail, Canadian National/GTW, Canadian Pacific, as well as there Delray Connecting RR and Detroit Connecting RR. My favorite spot is Delray, off of I-75. You get all major movements through the city, except for a couple CN trains and Amtrak. This is a very broad overview, shoot me a PM or email for specifics. Some pics of these locations can be seen on my flickr https://www.flickr.com/photos/ogauge47/
Wabash RR- starting at Oakwood Yard in Melvindale and heading west to Elkhart, IN where it connects with the NYC. About 10-15 trains a day. Canadian Pacific uses this line as well as NS
Michigan Line- Old Michigan Central. Detroit-Chicago line for Amtrak. Not many trains besides Amtrak
Detroit Sub- CSX Rougemere Yard in Dearborn to Plymouth, MI
Saginaw Sub- Old Pere Marquette line from Plymouth south to Toledo
Plymouth Sub- Plymouth west to GR. Virtually no trains
Conrail operates as the local terminal/switching agent in Detroit. They will use NS/CSX equipment but have their own crews, trackage and dispatching:
Conrail Detroit Line- main line into Detroit fro, Ohio. Starts at the end of NS trackage in Trenton and parallels the GTW Shoreline north, passing through Delray and ending at North yard in Hamtramck, MI. The Sterling Secondary splits off there to up to the auto plants in Sterling Heights.
Conrail Lincoln Secondary- Old PRR line connecting CSX in Carleton to NS just east of Oakwood Yard. Mainly used by CSX as a shortcut to Toledo, instead of running train on the Detroit Sub through Plymouth. Tracks are owned by Conrail but dispatched by CSX and maintained by NS....
CN Shoreline- Old DT&SL line starts at Lang Yard in Toledo and ends at Milwaukee Junction, on the border of Detroit and Hamtramck. Seems about 10-15 trains daily.
CN Holly Sub- starts at Milwaukee Junction and ends in Durand, MI where it intersects with the CN Flint Sub.
CN Mt Clemens Sub- starts at Milwaukee Junction and goes to Port Huron, MI. This single track line operates on Track Authority so there are no signals.
CN Dearborn Sub- Ex-DT&I from Dearborn Ford to Flat Rock, MI. A couple daily trains for the auto plants as well as coke trains for the steel mills.
Delray Connecting RR: operates in and around Zug Island hauling hot metal
Detroit Connecting RR: operates on old GTW trackage south from Milwaukee Junction and switches a few industries. Owned by the Adrian & Blissfield.