They already have that in the Barbarian vs. Civilized thing they have going on. It could go either way.
The central benefits of it though would be in providing the central Arthwydish with a way to accept the Cernn by "demilitarizing" the Cernn in a way that doesn't just force them to abandon the parts of militarism (aside from violence) that they value. Brotherhood (cooperative sports), accomplishment/heroism (obvious), and physical prowess (again, obvious). On top of that, having the Arête virtue spread with local Games would tend to promote the core competencies of a standing militia without having an actual standing militia. A squad of football players already have the teamwork training a squad of shield wall bearers need to be effective, for example. This could result in the Arthwyd unlocking/developing mundane technologies that enhance the performance of militias, which in turn would help offset the "bodycount" problem of the Caradysh Wights.
And the Barbarian vs Civilized thing could become a more entrenched part of our culture or end up magnifying itself.
The Cernn don't seem to be valuing a set of traits that happen to promote militarism so much as they value the militarism in and of itself. Which is probably the result of their long history of being attacked by other factions.
Physical prowess might be valued
because it can be used for the violence needed to protect the clan, heroism might be defined as the utilization of violence for the good of the community.
Likewise, the Arthwyd don't seem to be taking issue with the willingness to defend their communities so much as the fact that martial prowess is being used as a determinant of a person's worth instead of being an unfortunate necessity in an unkind world.
By helping the Cernn set up a core of career soldiers whose lifestyle is supported by the rest of society we would be leaving this desire for communities to have the capacity for violence intact while pushing the Cernn communities to value those who allow for the Sacred Warriors' lifestyle to be supported. Which validates the peace-loving Arthwyd way of life.
There are better ways of answering the Caradysh bodycount problem beyond throwing a larger percentage of the population at the problem. The most straightforward of them being research into improved divine magic or military tactics. Though fortifications or a larger population base would also be viable alternatives.
Now is not a good time to reach out for shinies. When we did the last Census, that would've been a good time since we didn't have anything demanding our attention and we were free to pursue shinies. Right now we have way too much on our plate to pursue side projects, even if the reward is an extra passive. (And that is ultimately a guess on your part. Personally, I see nothing that suggests you're right, and in fact believe that if it would get us a passive, our passive expansion would first expand to finish our provinces.)
1. The ice age is ending soon which means we're on the clock. If we don't get close enough to the Caradysh before it ends, we have to take values from the Cernn, which suck. More diplomacy is needed with the Caradysh.
2. We need to keep strengthening the relationship with the Caradysh. They have much to offer us if we have a good relationship with them, and a stronger relationship further reduces the chance of war with the very mighty peer power.
3. We have -1 Stability incoming from the Monarchists since we're not going to war, and -1 Stability from the Conservatives because with our Prestige it is impossible to get a new colony. We'll need to restore this Stability to keep making good but internally unpopular decisions and to keep the golden age counter going.
4. One of the big reasons the Arthwyd's remained stable and prosperous for so long is that it's made sure to keep its factions happy, but because of the above stuff, we'll be pressed for the necessary actions to finish the quests we can and want to do.
Once the Caradysh situation is settled, our Stability is stabilised and maximised, and we've caught up on the faction quests, we'll have free time again and can once more pursue shinies. Can be megaprojects, can be settling land, can be anything.
Claiming that now is not a good time to reach out for shinies while explicitly pushing for the shiny unknown that are Caradysh values and the known shiny that is a Golden Age is a bit hypocritical don't you think?
A 15/15 province might mean an extra Passive. Or it might mean an extra SEC action. Or it could even just mean an additional Province Action. As you pointed out, just because the 12/15 Province marker gave us a Passive doesn't mean the 15/15 stage will accomplish the exact same thing, even if you're taking that to mean that completely filling out a province has no benefits whatsoever.
1. The Maradysh were a valid target for Charitable Haven back when we took the Forlucan Bloodied, but Unbowed. As were the Raradysh, the Zaradysh, the Tordysh, the Lorvysh and the Forluc. All of whom we still maintain relations with. In addition, the Foreign Passive Policy may very well establish contact with other factions. We have absolutely no shortage of value targets if you hate the Cernnite values so much.
2. The Caradysh appear to be largely self-sufficient aside from their corpse import. And they are unlikely to be receiving support from the Arthrynite Pantheon when it comes to our divine magic. We have very little to offer them beyond metal weapons and tools.
2.1 That aside, diplomatic contact with the Caradysh has historically been bad for our Stability and Legitimacy. Given that we just took a stabhit and have some very angry factions clamouring for war, now is
really not the time for direct interaction if you're actually worried about Stability.
3. I am not opposed to a single SEC or a single MAIN Venerate. What I
am opposed to is trying to spend the bulk of our actions trying to fix the wrongthink of our population instead of actually trying to address the concerns of the populace or otherwise pursue productive goals. We've seen that type thing with autocratic regimes clinging to power, they are a poor example to emulate.
4. Unhappy factions tend to give punitive quests. And getting new quests while at low stability tends to result in quests that raise stability. We've dealt with low stability situations and unhappy factions before, we can do so again.
I'm just not sharing your desire for Caradysh shinies.