You asked, "Are there other more valid reasons for why maltose is polar or is that it? Or am I wrong?"
I concur with Mitch. Some other ways to get a quick answer for polarity (- not always correct) is to think about it's ability to dissolve in water. Usually, water dissolves polar and doesn't dissolve nonpolar. Sugar dissolves in water, so on a quick glance, it's polar. Other tricks: hydroxyl groups can point to being polar & symmetry - the hydroxyl groups on the sugar are not balanced out , which also points towards it being polar.
Again one of the best ways is to look at the structure and if it has dipoles, which is what you did.