I'm kind of moving in the other direction of having minimum education and intelligence requirements for voting. Not that this will solve 100% of the problems, but an educated, informed citizenry is necessary for democracies to survive. I'd say 75% plus of the population misses on one or both counts. If you're deciding who to vote for based on TV commercials, or even worse, just party affiliation, you shouldn't be voting. Point of fact, I'd love to see political parties banned. At the very least this would force voters to learn a candidate's positions. It would also get rid of the litmus tests each party does where anyone not kowtowing to the party line has little chance of winning a primary. In some states Mickey Mouse would get most of the vote if he had a D next to his name. In others Donald Duck would win big with an R.
I'm not sure mandatory voting would even be enforceable.
One change I would like is to move the system to online voting only. If you want good participation, make it as easy as possible. As for any concerns about security, we already have a security apparatus for financial transactions which largely works very well. No reason it can't be applied to voting.
Another thing is quite a few people don't vote simply because they use voting records (among other things) to make lists of potential jurors. I personally think we should do away with compulsory jury duty. Either go to an all volunteer system, or have paid employees whose job it is to serve on juries. Jury duty is one of the most hated and disruptive things expected of regular citizens. Based on some of the idiotic decisions coming from juries, I don't even think it's great from a justice perspective. In fact,
jury systems have been abolished in most countries for the reasons given in the link. Maybe it's time the US follows suit.
As for military service, if it's ever to be made compulsory it must include both sexes. That means everyone should have to register with the Selective Service, not just men. I actually read last week with the military running far short of its recruiting goals some are making noise about bringing back the draft. Politically that would be huge uphill battle, but now it has me worried. Would they give exemptions to people who are caretakers like myself? I might not mind having to fight for my country if we were in danger of being invaded, but who takes care of my mother if I do?
I couldn't understand why they were thanking me for voting--it's just what you do! Right? Well, that's what I thought until I saw the election returns--pathetic turnout. 
