Something that came to me. Let's imagine all 50 states had parliamentary systems instead of state legislatures, and thus could hold elections at any time instead of all 50 at once, like Canadian provinces and Australian states. We'll assume the maximum time between elections is 4 years. That's 48 months, meaning we'd have more than one election a month on average!
I do wonder though how many would be interesting, obviously Idaho and Massachusetts wouldn't be...unless the local Republicans/Democrats in each state split, which is most certainly possible. Actually I'd expect that currently ultra-Republican states would have to run against some type of Tea Party-esque splinter. I can see Kansas and Alaska having elections between some type of "Tea Party" and the Republicans, who on the local election would actually be closer to the state Democratic parties.
With states like Idaho and Massachusetts, this isn't necessarily true, if you examine Albertan provincial elections since 1971.