Honestly, I think 'metrics' are almost impossible to judge things by. The huge problem is that some bonuses can be shared if that race has a substantial number in the empire, some bonuses only apply if that race is the majority on a planet, some bonuses only apply to the troops of that race, and some bonuses are not sharable at all.
Basically, I think trying to attain perfect balance is foolish and impossible. I would be perfectly happy with 'Good nuff' balance, basically avoiding situations like the Atuuk whom have absolutly -zero- redeeming features to justify their suck. Even as a happiness-focused race they are lousy since their happiness is only 3rd best, beaten by the Securans and Shandar.
Here are my thoughts so far:
Ackdarian: Strong, gets the highest military ship size bonus in the game, bonus to colony construction, and very powerful ship maintenance/research bonus. Probably their only bad side is that their racial tech is not very good, but still saves you an enormous amount of RP
Atuuk: Weakest, their only bonus is a mediocre happinness bonus (+30%) and they have absolutly no redeeming features, even their colonies build slower
Boskara: Not sure, I am unfamiliar how war weariness works in this game, but the Shakturi Firestorm is an amazing weapon if you fight like the Covenant and prefer to glass planets as opposed to occupying them, since the Shakturi Firestorm enables you to build ships that can both fight off enemy defenses than burn the planet to a crisp
Dhayut: Worse racial bonuses than similar races, but one of the strongest racial techs in the game, the only downside is that im not sure the upgrades to that racial tech are worth it. You gain only an additional 50% speed but energy consumption doubles, might actually be betetr to stick to the initial tech if your worry is fuel efficiency
Gizurian: Decent. They provide ship maintenance bonus, high reproduction rates, hive mind, and, IIRC they will never generate a new leader which is awesome if you start with a really decent leader.
Haakonish: Very Strong, very similar to Ackdarians, except instead of a research focus they get an espionage focus instead. Their ship size bonus is also slightly weaker, but they get a special government and a much better racial tech. With Mercantile guild they can spam ships almost as well as Gizurians. The best jack of all trades race in the game, their espionage is strong, they can build lots of big ships, and even their research gets a boost with higher chances of scientists appearing
Human: Bad, their racial bonuses are not shabby but, to realize how bad they are, they only get an extra intelligence agent and a terrible special government while Haakonish get the extra intelligence agent, bigger ships, amazing fuel cells, and a decent special government
Ikkuro: Strong, ship maintenance, colony income, and troop maintenance, combined with RP discount on colonization techs, faster colony construction speed, and one of the best racial techs in the game. While not as amazing as Haakonish they are on par with Ackdarians
Ketarov: Strong, but a one trick pony. Aside from their espionage, they have no bonuses worth anything. However, their espionage is very, very, very strong. On top of the +50% bonus, they also get 3 extra intelligence agents which gets them a max of 9 intelligence agents total. They can wreck a lot of havoc with that. If you are a pirate, it might not be a bad idea to just exterminate these guys because otherwise they will incessantly harrass you with sabotage
Kiadan: Mediocre. Similar to humans in that they have decent racial bonuses, but no bonuses aside from that. Only thing that puts them above humans is Shadowghost ECM which is really, really good. But considering you can steal racial techs it might be better to just play another race and steal their techs.
Mortalen: Not sure, nice racial tech though.
Naxxilian: If you want the troop maintenance bonus, just capture a planet with this race dominant and build troops. Aside frmo that, they just have +10% tourism which is not that great.
Quameno: Strongest. +40% Research combined with Technocracy is just plain overpowered. They also have Novacore which is extremely strong early-game and while it is eventually surpassed by Hyperfusion, it still remains more fuel efficient (2 fuel points per 1000 energy points vs 2.5)
Securans: Mediocre. Strongest happiness bonus combined with a small tourism bonus and an insane reproduction rate. I am suprised they do not have an espionage bonus, even a small one. Its is sort of odd that they are just simply better than the other two happiness races, Atuuk and Shandar, but still fairly mediocre.
Shandar: Bad. Not Atuuk levels of terrible but their only unique feature is the spaceport armor bonus, which I am not even sure works.
Sluken: Not sure, but I really like the Starburner, they also get faster troop regeneration which is also unique to them.
Teekan: Ok-Decent. Bonuses to mining, trading, and colony income which, alongisde merchant guild, lets them print money. Only downside is that they get a military ship size penalty. An interesting strategy might involve turning their civilian fleet into armed merchant ships, setting their AI accordingly, than have the merchant ships do most of the fighting. With extra civvie ship size you might even be able to build ships on par with military ships.
Ugnari: OK-Decent. While, on first glance, they are watered down Teekans, unlike Teekans they do not get a penalty to military ships and they get a very nice racial tech, Raptor Targeting. A good pick if you want a merchant-focused race but not overly so like the Teekans.
Wekkarus: Not sure. Never used/experianced wave weapons, and on paper they are money-focused but without Merchant Guild or any trading bonus. I never see them do much in my games.
Zenox: OK-Decent, If you want proof that Technocracy is overpowered, this is it, aside from technocracy the Zenox are not that great, a small ship maintenace, happiness bonus, historical locations and megatron Z4. Megatron Z4 is probably the best of those bonuses, it is absolutly amazing early game but late-game Meridian shields probably are either better or worse, depending on weither you like shield regen or shield capacity. Historical location knowlege is useless because historical locations are extremely easy to find as soon as you get long range scanners
I ate the batter of the bulge at Hans' Haus of Luftwaffles