Are there any can't miss places between Michigan City, IN and Muskegon, MI?
If you happen to be passing by New Buffalo around lunch time, pop in and experience PierreAnne crepery. It's a small place owned by, of course, Pierre and his wife Anne and it's wonderful. The savory crepes are out of this world. I'm a meat and potatoes guy and I rave about this place to anyone I can! Please consider it; you won't be sorry.
If you are going through Muskegon, you absolutely must stop at the Hearthstone Bistro.
You can visit their website at http://www.hstonesoup.com/. Every meal I have had there has been wonderful, and they are well-known for their superb soups. They feature three or four soups every day I believe, and my boyfriend can't get enough of their french onion soup. The waitstaff is always awesome too. I worked in restaurants for seven years in many different positions and I have high expectations when it comes to service and the Hearthstone has never let me down. If you will be there on a weekend you may want to make a reservation beforehand. My boyfriend and I drive over an hour to get to the Hearthstone Bistro for special occasions because it is just that good. They also have a very nice outdoor patio area.
3350 Glade St, Muskegon, MI 49444
EPC always, rightfully, gets raves (and I don't just say that because the owner came and pulled my Jeep out of a snowdrift after our blizzard this past winter) so I'll go different direction. Depending on when you come through, Douglas has a fun little place called M&M/Blue Star Cafe, it's an ice cream place that also has sit down restaurant with really good lunches.
141 Blue Star
You beat me to it, so I'll just second the recommendation of Everyday People. For my money it's the best restaurant in all of western Michigan. I posted a detailed report back in 2007 in the Saugatuck topic at http://chowhound.chow.com/topics/413534 I've eaten there several times since then and it continues to be superb. Note the caveats in that report - they don't take AmEx; they also don't take reservations, and waits for a table can take a while in season unless you get there early.
Everyday People Cafe
11 Center Street, Douglas, MI 49406