Sorry for not being clear here. What I meant is that Spiritualist cannot get the happiness yield bonus outside of the capital by itself.
Ah, I better understand you now.
You need +20% happiness until you get your first (+10%) yield bonus. So, okay, you now have +10/+15% with a spirtualist race. But you still need a secondary source to get yield benefits outside your capital. If the happiness systems worked in 5% steps, spiritualist would probably be a decent all-around ethic (and it would probably be even worth giving up robots for a generic +2.5% or +5% happy yield boost in the early game).
Although I guess that would sorta compensate for the Robot happiness penalty. Maybe that would be enough to move Spiritualist into the "Situational" category.
I'm having a lot of fun with Fanatic Spiritualists with the communal trait, because that hits the 20% marker giving all my colonies +10% to all tile yields pops right off the bat, but yes, it does require a significant investment: 2 of 3 ethics points and 1 of 4 trait points.
I've only had the game for a week now, so compared to your beta experience my experience is necessarily limited, but I've primarily been experimenting with different forms of Spiritualist and Fanatic Spiritualist governments (with a single Fanatic Materialist to provide comparison data) and so far they seem to work really well when focusing on growth to compensate for weaker tech than Materialists.
All combinations have Adaptive, Communal, and 2 negatraits. So 20% happiness (10% ethics, 5% trait, 5% grand design from Void Clouds) so long as they stick to their ethics, with aliens getting 5% happiness (and 10% extra if they are successfully brainwashed to your ethics over time).
Fanatic Spiritualist/Pacifist, Enlightened Monarchy: Rerolling until I got a charismatic edict discount ruler. The most absurd early game growth I've yet experienced. Everybody happy or, once Paradise Domes were researched, joyful. Every planet affected by the Fanatical planetary food edict in the crucial growing stage before they turn into full-fledged colonies without ethics divergence penalty and with access to better buildings. Who the hell needs robots? Transitioned into an equally strong mid-game and even stronger end-game. (By the time of the death of the first ruler the kingdom had already gone Irenic Monarchy, so the loss of the ruler edict discount was only a minor setup, and by this time the edict cost reducing techs were becoming available as well making it even more absurd.)
Fanatic Spiritualist/Individualist, Theocratic Republic: Lots of energy and the Theocratic Republic's ethics bonus counteracts Individualist. Like the pacifist variant, everbody joyful once the unique building built. It worked nicely, but not really my thing due to Individualists' restrictions.
Fanatic Spiritualist/Militarist, Theocratic Republic: Granted that Militarist is pretty weak, but... what does this grant you, apart from avoiding the restrictions of pacifism and individualism? Well, you get the same +20% happiness that makes your homeworld joyful and puts your non-homeworlds at happy. But your unique building only produces 5% happiness, so you are 5% short of what's needed to take advantage of the Adaptive trait, whereas the others are joyful as soon as they build their special buildings. War, what's it good for, they ask? I tell you,
another 5% happiness, that's what. So as long as you are at war your non-homeworld native planet type colonies will ALSO be joyful! And it gets better. If you are making war in the first place, you will want to conquer your enemies and make them into upstanding citizens, not slaves. (Because you aren't a Transcendent Empire, duh.

) Fortunately, Theocratic Republics are rather good at that. Once you transition to higher government you get -35% ethics divergence (20% government, 5% combat arena, 10% edict - and yes, -5% research speed is totally worth it) to combat sector assignment (10%), distance, and any unhappiness penalty. (Also gets more mileage out of PSI warriors than the other types

)
Of these the Pacifist Enlightened Monarchy is probably the strongest, but the Militarist Theocratic Republic the most fun to play. It really encourages an active playstyle.
That all three have greater than normal core sectors is a very nice bonus; not sure I should consider it fringe bonus rather than a major bonus in its own rights given the current inadequacies of the sector AI with respects to developing planets, since the larger core sector makes it much easier to assign several slots to raising planets to planetary administration level (5) and ordering necessary buildings before handing them over to a sector.