Something I realised:

The laws make mention of it being forbidden to drink another Vampire's blood... but then doesn't mention anything about what happens if you do.  

Maybe that'd make for an interesting Truth? "The effects of hemocanabalism"?

As others have mentioned, more Truths would be good. Rather than the "all or nothing" truths there currently are, maybe some middle-ground truths would be good? Something like these, perhaps:

What Mortals Know:

"Most people don't know of the existence of vampires, but there are certainly organised, albeit small, groups. Vampire hunters are certainly a real threat, but much like vampires themselves, often isolated to a particular location. There may be fringe sects of particular religions dedicated to hunting vampires, but are not under any sort of central command."

Genealogy:

"Vampires generally develop similar abilities to their sires, (A nature drinker is usually sired by a nature drinker, a seer is usually sired by a seer and so forth. Additionally a vampire will always share at least one power asset with its sire, even if they don't share natures.), meaning it is generally possible to track an individual vampire's 'ancestry', but lineage alone is no indicator of a vampire's powers."

Factions:

"Because most of the risks associated with moderate or even long-distance travel have practically disappeared vampire city-states are generally a thing of the past. Though a global vampire society is a long way off, any individual Queen may rule an empire of multiple cities, and even come into conflict with rival Queens, such empire borders often coincide with human ones, at least where hard borders exist. "

Superstition:

"They're not superstitions per se, but they are exaggerated tales of half-remembered anti-vampire folk knowledge. Garlic's odor is unpleasant, 'true' religious symbols are consecrated in a way mass-produced or jewellery-style ones aren't, Vampires can enter private domains uninvited, but specific entryways can be supernaturally 'barred' to vampires. Stakes however are just sharp sticks. But enough peasants with enough sharp sticks..."

Werewolves:

"Werewolves are simply mortals with a different type of beast in 'em that must be fed. Though less common than vampires, all cities will have a few loosely organised 'packs', dedicated to keeping each other safe and keeping their secret from humans."

Elegy played a crucial role in sparking my interest in both solo and co-op gaming. Its accessibility made me feel capable of playing without being overwhelmed by too many rules.

Now, I occasionally mix things up by incorporating Ironsworn moves and rolls, all while using Elegy themes, complications, city events, clues, ambience, assets and more. Santa Maria by Night truly comes to life with the way you have structured the background, locations, and tables.

Any upcoming additions, in any section, would be eagerly anticipated. Perhaps one suggestion is to include more resources to aid the fiction and investigation, offering further methods to push the storyline in different directions or to find out the narrative consequences of bad rolls.

Probably more world truths(and maybe have some story seeds/starting elegies under those world truths as well as the clans and factions)…

just an idea though