You've got a habitability boost. Not that that means much, because neither of you care about happiness to begin with.
You're still technically a Machine Empire, so a lot of stuff targets robot build speed. But you still have semi-organics with the Cybernetic Trait that don't eat and grow normally and can be leaders and such. You don't get food boosts, because neither of you use food. Rapid Breeders should still work, though. I guess you have to think about how much you want to use the robos and how much you use the people, and what for.
It gets more confusing given the Paradise Dome version for them. No happiness, but 15% to energy and mineral output for Cybernetic pops(So anywhere from +30 with just Industrious, to +40 Industrious/Very Strong. An organic could get it higher with +happy, but he'd need Social Welfare/Utopian standards, which would tax his minerals in Consumer Goods anyway. But it'd mean better results in Energy and Science. Energy…15% Thrifty for both, Corporate Dominion gives the organic shooting for Energy +10%. There's no similar civic for Machines. Happy is potentially 15-20%. But that's presuming the organic took Communal-happy is not easy. Hmm.), and the only building in the entire default game that exploits both Energy and Minerals- +2 to each.
Still, no one biological actually likes you between either 'Dreaded Assimilators' -100 or 'Soul Thieves' -200 for Spirituals, and you've no direct combat boosts to draw on. Warbots maybe(But Rockbreakers is probably better), Strong/Very strong, and your cyber admirals get 5% +fire rate. But your Robo leaders are immortal barring accident events or being killed in combat. Hmm. Uncanny might be a free pick, but what if there's another Machine you can hook up with? That -25 would hurt-you've probably enough enemies as it is.
Doing what you're meant to do and assimilating gives you unity and….society. I mean, yes, it improves your understanding of biology and culture and armies-hooking all that up into you isn't easy. Maybe it should give you points in a random area, though?
Can Cyborgs live on a Machine World?
Maybe there's someone who can speak further?