....Usually when I am looking to add/remove something, I look at the lore and the victory conditions, and try to do something that would fit that race.
Sounds like a good approach to enriching the game and player experience.
For example, I removed the Gizuraens permanent leader as, VCs aside, the Gizureans are specifically mentioned to be a divided and tribal bunch. As a race their OPness is a three-legged stool with the permanent leader as one leg (on top of this their leader starts with 4 really good skills), high growth rates as the second leg, and the ship maintenance bonus as a third leg.
What? What is wrong with the bug god-queen mother (or whatever title you please) having a very long natural lifespan that goes beyond the game's duration?
Though I still like the idea of permanent leaders so, for now, I gave it to the Zenox. Their research took a major hit when I nerfed Technocracy (they are behind Kaidians and Humans), and I really could not think of anything else to add to them without making them too similar to another race.
And their lore is ... a cyborg scientist-administrator seized imperial power?
A zeal for balancing is appropriate in a competitive game that is supposed to be fair to all players (though balance only has meaning with given starting conditions and consistent rules and is roughly confirmed with statistical analysis). Examples would be handicapping of races or balancing the pricing of "purchased" attributes or items. It is a daring ambition.
Attempts at rough leveling in a very sophisticated game seem procrustean here. This topic is about the "best" starting races, not about how to change the game to ensure none can be best.
I may be wrong, but I understand there are already dynamics among the empires that react negatively to amassing power, aggressive expansion, etc. and this is a natural check. If one race becomes much more advanced technically, its tech may be stolen or copied from captured ships. That is another check. Temples, ancient ships and other fun surprises across the galaxy can tip the balance at times and certainly mix things up.
Handicapping victory conditions is a good way to make things fair in multiplayer without unsettling the gameplay, as well as to add the right flavor and incentives.
I think the best way to do this would be to create some basically "blank" races with lets say one bonus.
Equalizing Pop Growth across all Blank races, except for the Race intended to test the efficacy of Pop Growth.
Now, this kind of experimentation I can appreciate as useful for players to understand how the mechanics work and that they work consistently.
Best we can probably hope to do is buff the weaker races some and nerf the stronger races some, probably looking at it on a case-by-case basis. It wont get perfect balance, but a reduction in strength differences between the strongest and weakest races would be enough to make me happy.
No, the best most of us can hope is that needless MMORPG-style nerfing and buffing does not happen, but that instead bugs are addressed and the mechanics, events, and other aspects of each race are richly and effectively implemented.
Which is not to say that mods can't change whatever they wish, but we need to be able to trust the essential stability and continuity of the basic Universe (and for me Extended along with that, which does not disturb the existing races).