Debs ran from prison (for the high crime of telling people that WWI was none of our business and people shouldn’t enlist to get turned toa pink mist in Belgium) in 1920
As for voting as a felon, that varies state to state. I don’t think there’s anyplace that allows people to vote from prison, but quite a few states let convicted felons vote once they’ve completed their sentence and any parole that follows it (and in some states, pay additional fines, which sounds a bit like a poll tax to me, but I’m not one of our nine kritarchs, so what do I know about that sort of thing?)
As for people running for office when they couldn’t vote, Elizabeth Cady Stanton ran for office well before she could have voted, and the first woman elected to Congress (Jeanette Rankin) was elected in 1916, several years before women’s suffrage was added to the constitution, though her state, Montana, had allowed women to vote already.
Every vote for Biden in Steubenville is another vote that somebody in Cleveland doesn’t have to counter, so yes, vote.
The electrical vote is state by state (with two states, Maine and Nebraska divying all but two of those votes one per congressional district), so your vote in a swing state matters.