On a purely systemic note, the first-past-the-post US voting system would benefit immensely from ranked voting, which in most forms makes it impossible to waste your vote if you choose a minor candidate.
As an Australian, I also think mandatory voting would fix other problems with the US electoral system, like perceived voter fraud (since most of the population votes, to cast a vote as someone else is harder and more easily detected), access to polling places (since it's a more obvious and immediate injustice to fine someone for not voting at a polling place with a three hour line than to merely deny them a vote), and the election of presidents who didn't have anything close to a majority of the population voting for them. Mandatory voting is much more controversial than ranked voting when I bring it up with Americans, though, and a less important fix.