Strictly speaking, you only need to think there's a 51% chance that Trump wins FL by <8% to make that bet +EV, assuming you have the bankroll to tolerate being a degenerate gambler. Silver didn't need to be 100% confident to make that bet. Obviously it backfired, but he literally is a gambler, he played poker for a living before online gambling regulation got him involved in politics, it's not surprising he would take what he had reason to believe, based on his past track record, was a +EV bet. Sometimes you go all-in with a full house and get beaten by a royal flush, but it doesn't mean your play was incorrect, statistically speaking.

> for which "well, 80% of the time I'm right" is useless in terms of actionable information

I mean, this is basically how weather forecasts work too. Would you say that weather forecasts are useless? I don't think they are. I think the existence of weather forecasts results in people being prepared for rain more than they otherwise would be, even if sometimes they neglect to bring an umbrella because the forecast predicted a low chance of rain. In the same way, political forecasting is actionable in terms of how politicians and their parties conduct their campaigns, focusing on areas where spending their time, energy, and campaign funds will get the most reward for their investment. I suspect a political party that makes use of forecasting will outperform one that doesn't if all else could be equalized. As for benefits to the general public, one of the big reasons Silver got into forecasting was to counteract the exact thing you were talking about earlier - he hated pundits crafting a narrative and trying to influence public opinion on elections baselessly, so his goal was to establish a more objective, numbers-based approach that was less susceptible to people just making shit up about elections.