Not much is known about this subject, mainly because most sages are not prolific seed producers, and it is hard to harvest, since ripe seeds generally disperse shortly after they ripen.

Those with dense spikes and especially globular heads offer the best prospects for bulk seed. The globular heads might become tumbleweeds once the heads fall off. The related genus Monarda uses this dispersal tactic, and seed is spread out over a wide area because of an annulus of hairs in the calyx tube that prevents all of the seed falling out all at once. Salvias in general don't have that retaining ring of hairs in their calyxes.

Seed dispersal in most sages is aided by a glutinous coat, which swells up when moist and allows seeds to be carried about by sticking to insects, birds, and animals.

I was thinking about Salvias with larger seeds like regla or spathacea. They might be more worthwhile to harvest.

It's always interesting to know what's edible in the garden.

I'm afraid that spathacea doesn't produce enough seed per plant and per square footage to be of more than medicinal value. Salvia regla, as a shrub or small tree, is a bit better, but you would starve given the amount of seed you could harvest calyx by calyx each day.. It took me about three weeks on my Mount Emory to harvest about 200 seeds. If you had an orchard of them, you would find more seed, but the intensive hand labor would be prohibitively tedious, unless you were a seed-eating bird.

Now if you were myself, Robin Middleton, or Rolando Uria, it would be worth your while to collect a couple hundred to a couple thousand seeds of each salvia for distribution to other collectors, botanical gardens, nurseries, and scientists to preserve these plants for their own value, enjoyment, and research. I used to collect seed, and I can appreciate the jobs that Rolando and Robin are doing. Their efforts are very high value, and the fruits of their labors need to be shared.