At one time DKIM and SPF were good indicators that an email was spam because spammers adopted it so that their mail looked more legit.

I never look at DKIM or SPF. If I really care about who a message comes from I use PGP. It's a handy input for learning spam filters that use it as one piece of information, but it has about a 10% failure rate (legit mail where the signature fails to verify because of message manipulation in transit). It's most useful if the domain it's matching against is also trusted in some way. For example, a good signature against google.com is likely to mean the mail is good; a good signature against frohfuwehfwo.biz is not very helpful unless we know that that domain always sends spam.

Also, the most important piece of mail I ever received (from the Prime Minister's office) came without SPF or DKIM and I authenticated it by calling the office. In general, external authentication like that tends to reassure me.

Plenty of crappy DNS web admin "tools" limit the maximum length of a TXT record. Sometimes it's harder than just typing "1024" instead of "512"...