I agree with the OP, go ahead and do it -- it will bring alive lots of American History. AND you'll get to read about much of the history several times, as President's lives start before they are elected, and continue after they are. So you'll get to read "the rest of the story" on different political issues as you work your way through several lives. I'm a serious 19th century buff, and I gained a much deeper understanding of the causes and consequences of the Civil War by reading biographies that started way before the war, and those that ended far after the war did.
For those who are interested in the idea, even if you don't have the time to read all the president's lives, CSPAN has a series entitled "The Presidents" (and a companion "The First Ladies"). You can view them at your leisure by watching the free, live streaming video on
C-SPAN.org | National Politics | History | Nonfiction Books. The idea for the series is that they get two or three of the very best living historians who have published bios of a particular president, and get together with them at a site associated with that president -- usually a presidential home, though sometimes the presidential library or a birthplace. They film for three hours, give a short bio, and then open up the phones to callers nationwide. The historians have to field all these random questions about the presidents, their lives, their politics, scandals, etc. They break it up with short tours of different parts of the presidential house, or showing something important to the president (like souvenirs of his presidency, etc.). Unbelievably riveting television, because you never know what the callers will ask, and the historians know so much about their presidents that they can take a short, uninteresting question and spin out fascinating tales. Yes, I can honestly say that I listened on the edge of my seat to hours of television about Millard Fillmore, Martin Van Buren, Grover Cleveland, etc. The series was such a success that a few years later they repeated it with "the First Ladies." Can't say enough good things about this.
Go ahead and get started with your bios -- but you may find that some presidents have so many good bios that you end up reading more than one!