I wouldn't suggest going overboard on the blueberry additions. These muffins have the perfect amount. Fresh and juicy blueberries are just that... juicy! If you added much more, the batter will be too wet and gooey from all of the excess liquid the extra blueberries bring with them. And you'll have a hard time getting your muffins cooked all the way through before the tops of the muffins burn.