Mandatory voting seems a bit extreme. Maybe the first step would be to join the rest of the world and have two or three voting days and have at least one or two of those days on a weekend. Some countries give a day off work, which isn't a bad idea either.
The people who are presently not voting, by and large, don't vote because they don't care enough about who's in office to bother voting. I don't think we can expect these people, if forced to vote, to put any significant effort into deciding who to vote for.
So who benefits by forcing them to vote? Would it just be random? Or would certain viewpoints/candidates be propelled by ignorant, disinterested voters?