If you're getting mail spoofed from someone else's domain and they don't have SPF, adding SPF to your own domain isn't going to do anything (I've seen this suggested.)
Additionally, if someone is getting spoofs from your domain and your SPF is correct, they're not filtering on SPF.
At the end of the day, SPF, DKIM, and DMARC only matter if the recipient's filter is actually checking those and filtering accordingly.
