If they all did, much would be different.People my age could also vote too, I know I didn't this year.
Assuming that most millennials lean left (which they do), then yes, vote Democratic, or Green. But don't discount the primaries. That's where the Tea Party has moved the dial most effectively. If all millennials voted, Dems would be falling over themselves to demonstrate their liberal credentials. Elections are an evolutionary process. Votes are environmental pressure.
I don't think it'd happen in one election cycle, but if you change the political landscape of your local or state government than you'd be picking people that you felt were honest or educated to hopefully become career politicians. Fuck if I know who ran in my city/state this year though, so I don't know what the canidates looked like.