SPF/DKIM aren't meant to solve spam directly. They are aimed at sender forgery.
The real benefit of SPF is for outgoing mail. People no longer forge my domains. It stops backscatter. It has almost eliminated the mistaken spam reports to my ISP by people who don't understand mail headers.
The real benefit of SPF is for outgoing mail. People no longer forge my domains. It stops backscatter. It has almost eliminated the mistaken spam reports to my ISP by people who don't understand mail headers.