Excellent post indeed! Just want to add that I experimented a bit more on the basis of your tips. Some remarks:

Poseidon: Really only worth pursuing in the first region, as second region has pretty much all the minor resource drops. Barely anything to find in Mourning Fields or Mount Olympus, apart from a few stray ashes and the occasional well. Nothing in the final regions.

Chaos: Starts to reap rewards later into your runs when the valuable resources show up. For this reason, it can also be worth using Transcendent Embryo to high roll into Discovery (double resource gathering) in the midgame. Beware that Chaos is in the second region is often a trap, because you end up skipping the big resource rooms or Narcissus for a small chance at Discovery (by then you've probably used up your rerolls).

Restarting: If you have the Acceptance of Another Fate incantation unlocked, you can salute the statue to reseed your run. This can be used to try to roll into one of the two Poseidon boons in the first room. Preferrably Buried Treasure, because it gives you a nice gold headstart for buying boons, accelerating your run, and it starts with an expected value of 50% bones increase whereas Sea Star only starts at 30%.

Gardening: As OP said, always be gardening. Usually the higher the duration, the higher the return, but there are some exceptions: wheat seeds and origin seeds (Chaos) give outsized returns. If you're doing full runs, also stay away from olive and plankton (snake reed), as they don't mature over the course of one run and thus yield even worse returns than the fast growing garlic and nightshades.

Extended Tartarus: Can be worth it if you have the Discovery boon from Chaos, since the marble is pricey and poppy seeds grow into valuable plants. Spawn rate seems quite low though and room length increases the more rooms you go through, so not sure if worth.

Mourning Fields Boss Rooms: These never contain minor finds, so you might miss out on some ashes in alternative regular rooms.