Manchester was my neck of the woods growing up. There's a fish hatchery just east of town that's great for kids. Whitewater Park is on the Maquoketa River near downtown if you want to go tubing or kayaking. You could also check out the Franklin Street Brewing Company. That's about it for in-town attractions There are some other places to see outside of town, but within 30 minutes. Backbone State Park (the oldest state park in Iowa; 15 minutes straight north) and the Lake Delhi Dam (15 minutes SE; breached in 2010 and rebuilt in 2016) come to mind.
Manchester actually has quite a few restaurants for it's size, but none of them are "must see" places IMO. There's Dairy Queen, Subway, Pizza Ranch, The Sunset, and Godfather's Pizza on the West side near the Walmart. There's a few mom & pop places and a Burger King & Hardee's across from each other downtown. Lastly, on the East side all by itself is a Pizza Hut. The DQ used to be right next to it, but moved to it's current location many years ago. I've eaten at the Sunset in Manchester a few times and thought it was very good and reasonably priced.
Breitbach's claims to be the oldest continuously operating restaurant & bar in the state of Iowa. It's been open since August 23,1852, but they had two fires within 10 months of each other in 2007 & 2008. It's still a good restaurant, but not as good as it was before the fires. It's not worth the 50 minute drive from Manchester unless you also want to check out the beautiful scenery overlooking the Mississippi River on the NW side of Balltown.
As previously mentioned, Dyersville's about 20 minutes straight East on Highway 20 and there's much more to see there. They have the Field of Dreams, National Farm Toy Museum, Plaza Antique Mall, and the Basilica of St. Francis Xavier.
If there's one place you must go to try the food, it's Chad's Pizza in Dyersville. The dining area is small, but their pizza is amazing. It's on the same level as the Wig & Pen in Coralville IMO.