I haven't gotten a chance to play all the races yet, but I just got done with a godlike Arceans game and I had to share. These guys rock. It's like their bonuses are all in areas that really matter, and the synergies between the abilities are just lethal.
You need to get your hands on Techapods to really use Arceans. And as much Xanthium as you can get. Rare black holes in your map settings help make it a more decidedly Arcean game, because that makes your special +Move structures stand out.
What's cool about these guys is:
a) Starbase range starts at 6 instead of 5, and that includes mining. More resources with less administration.
b ) Straight up military bonuses
c) Military bonuses...inside of your starbases' expanded ZOC...in addition to your standard military bonuses. Territorial Reinforcement tech, which gives +5(!) to all three defense stats inside of a (expanded) starbase ZOC, for cheap. Military starbases get a 10(!) radius after you go up the Pragmatic line.
d) Access to Navigation Centers, Stellar Forges, and Weather Control, which are all cool in their own right. And Temple of Valor, but Temple of Valor requires Xanthium, and you need the Xanthium for Stellar Forges.
The power comes in the synergy you get when you combine the expanded starbase radius, with the extra starbase ZOC bonuses, with the expanded starbase radius from Pragmatic. It's nuts. On abundant/abundant planet settings, I'm getting 6 or 7 planets inside of a single economic starbase. 4 precursor relics inside one starbase. Entire empires inside of one military starbase. The production bonuses from economic starbase + Manufacturing relics stack with the +15% raw production bonus you get from Weather Control--which you can build instead of Intimidation Centers, because you are going Pragmatic.
The Navigation Centers/Galactic Navigators Guild give wicked +2/+3/+4 movement bonuses. Hyperspace Project? What's that? Who cares?
Stellar Forges synergize with Medium/Large/Huge hulls, because they're giving +10% free hitpoints and -10% maintenance, stackable, for each planet w/ Stellar Forge sponsoring the shipyard. 600-hitpoint huge hulls. And you're not giving up production on your mega-production planets, because the Stellar forges give +1 social/ship construction adjacency bonus just like a Factory (if you park it next to a Starport/Deep Core mine), AND a +1 research adjacency bonus in case your neighbor is a lab. It just takes a little positioning to work around their lack of an "All Construction" adjacency bonus. But it's not too hard.
Tiny hulls even get into the play, because Stellar Enhancement is not that far up the Tech tree, and it gives +4 hit points, flat. And those tiny one-turn-wonders synergize with starbases which are giving +5 to all defense stats. You don't need engines, because hello, Navigation Centers.
There's just powerful synergy all around with these guys. One thing to realize with starbase range is, a +1 range bonus is a bigger deal when going from +6 to +7 than it is from +5 to +6. Think of the area within a circle: Pi*R^2. The area your starbase encloses goes up non-linearly--with the SQUARE of the range. In spite of this, I'm using up Administrators like nobody's business--not because I HAVE to, but because I WANT to. Simply because I am getting so much done with starbases. Why burn a Leader on a 6% bonus when I can get a relic? The 4-hex minimum distance between starbases remains the same, even though your starbases extend farther.
Finally, there's Mercenaries which give bonuses when you park their ships on top of a starbase. You get twice the mileage out of them with Arceans.