For a more concentrated maple flavor, use grade B maple syrup and brush with additional syrup when warm, if desired.
Make the streusel: In a medium bowl, combine oats, butter, sugar, salt and flour and work with hands until mixture is no longer dry and large clumps form. Add maple syrup and mix to combine. Cover and refrigerate.
Make the muffins: Preheat oven to 400 degrees with racks in upper and lower thirds. Line 2 standard 12-cup muffin tins with baking cups. In a medium bowl, whisk together flour, oats, baking powder, baking soda, and salt.
With an electric mixer on medium speed, beat butter, maple syrup, and sugar until pale and fluffy, 3 to 5 minutes. Add eggs, one at a time, beating well after each addition; mix in vanilla.
Reduce mixer to low. Add flour in 3 additions, alternating with 2 batches of yogurt; beat until combined. Transfer batter evenly amongst 24 muffin tins (a scant 1/4 cup per tin). Remove streusel from refrigerator and break up into small pieces. Scatter evenly over the top of the muffins. Bake, rotating once, until tops spring back and a toothpick inserted into the middle comes out clean, 16 to 18 minutes. Let cool 5 minutes in tin, then transfer to a wire rack to cool completely. Brush muffins with more maple syrup while warm, if desired.
For consistent distribution, use an ice cream scoop to divide batter amongst tins.