Thought: if you're going to increase the oats by half a cup, do yourself a favor and also increase the sugar. If you don't, guess what? Your muffins will taste like plain oatmeal.
The good news is that the increases (half a cup more oats, half a teaspoon more baking powder) achieved the desired consistency. They are now high and much more dry... more sugar (white instead of the brown already used, I think) will solve the "blahness" problem.