Not a farmer, but I believe they use weather derivatives to hedge and weather forecasts for predictions? Going through markets for weather forecasts is adding a level of indirection that generates a noisier signal.

The idea when hedging isn't to win on expected value. It's to reduce risk. You're paying the market to provide insurance.

As a side effect, insurance does sometimes generate interesting data. The insurance industry generates good data about life expectancy. But it doesn't tell you when you're going to die.

Sure, but I meant it in the sense that someone needs to lose money or there's no point in smarter or more well-informed people playing. Their profits have to come from somewhere.

These could be (a) people who aren't as smart as they think they are (b) people who subsidize the market in order to get good predictions (c) people who are hedging (essentially, buying insurance). Perhaps other possibilities.

But usually when prediction markets have shown interesting predictions, it's by odds taking large swings then collapsing to the correct outcome relatively shortly before the event right?

I assume because even if you know the future perfectly, putting up large lump sums early could cap your upside if people take your large sum as a signal (like OP is doing)

As a viewer you can take your own short-term "actions" (gambles) outside the market using the brief advanced notice I guess, but I'm not sure planning works like that.

In other words, what happens to the accuracy of prediction markets if we're including the discrete odds that occured along the way to the final odds? It's not better than random chance or public sentiment for large events is it?

Equating being "consistently right" with having a sufficiently large stash of capital is ludicrous.

"right" people will wisely take most their winnings out of a high-variance market. "wrong" people with deep pockets (or lots of wrong people with shallow pockets) will continue to distort the market.