By that reasoning nothing is worth the effort. You are trying to design
a silver bullet; we already have acknowledged that there was no such
thing. MARID/LMAP/SPF etc are to become one out of 20 or 30 items in
mail handling. Look back in a recent past: there was a time when RBL
lists were the solution. Then the spammers adapted. Then came Bayesian
filters and many people touted them as "the" solution. Then the spammers
adapted. MARID is not going to be the silver bullet that will stop spam.
MARID will stop 20% of spam in the beginning and 5% in the end.
The difference here is that MARID has the potential to be a platform to
base the next round on. Bayes doesn't leave you much to grow on, nor do
RBLs -- but MARID lets you move the checks up a level, checking the
domain's trustworthiness against reputation lists, or even just RHSBLs
listing the most egregious violations.
Ari