Compulsory suffrage is a downright stupid proposition in America. The only Americans that vote are those that are interested in politics, and old people. And, generally, even those voters are too stupid to make decisions. Now, if you force the entire partially-mentally challenged populace of America to vote, the results would be even worse. Look what the perversion of democracy got California, for example.
In fact, if I were going to change voting restrictions in any way, I'd restrict them. First, only land (condos, houses, land, etc.) owners can vote. After all, land-owners pay the majority of the taxes and take the majority of the risk involved in the economy, why shouldn't they get a greater say? Second, restrict the voting age to between 18 and 60. After 60, you aren't going to live more (on average) than 15 years longer. Thus, since you no longer have a stake in the future of the nation, why should you have a SAY in that future? Third, if you have a criminal record, with ANY FELONY, you're no longer allowed to vote in ANY election. Probably not a problem. Most people who commit felonies don't vote anyhow. Finally, administer some, at least, basic IQ test. Do you honestly think that it is fair that a burnout or just plain stupid person, has the same say in the government, or the insight to use that voice, that someone like Albert Einstein does (or did, in this case)?