SPF and DKIM no longer have any real value. Just look at SA and the values it assigns by default to mail with those headers. Couple that will the fact that spam now has valid SPF and DKIM - just makes them pointless.
DKIM and SPF, along with DMARC are more about authentication - they let you know that the message has come from where it says it does. This makes spoofing harder, not necessarily spam. Greylisting deals with most of the "spray and prey" spammers, though it does have it's own issues.