Okay, Stardock is brilliant.
Unique Research Trees, so the Humans seem more like Humans and the Dark Yor more like...Dar Yor.
Lets take this one step further.
Why would they then have the same senate and political parties?
Sure, if you start an Imperial Republic, maybe there are certain commonalities, and some races may have similar governments.
However, what I see is an evolution with Arnor;
Lets take the Korath and the Drengin.
Lets say in the Drengin Empire, you turn each political party into "Clans". However, you include a Drengin Clan and a Korath Clan in both races.
The Political Parties function much the same was as they do now for them. The player picks their political party, the "Korath Clan" for instance gives you +20 to research and +1 to sensors. Okay, awesome, just like political parties. Whats the big diff?
Well, if the Korath Clan controls the Drengin empire ruling body, they become their puppets and vise verse. You can use your "Agents" to assisinate ruling members of the Clan and/or circumvent with your own. Also as you have research treaties and borders with them, they naturally grow in strength in that clan.
Other Clans also could emerge as you build up things. For instance if there was a "Ferran Clan" and this was essentially the mercantilists. Each time you build up your black markets, you are adding one more to the Ferran Clan.
Instead of a Vote, there is a combat that happens. The biggest, baddest champion is selected from all sides and fight. Whoever has the strongest party will have the biggest champion but since the game randomly determines the details of the gladiatorial combat, its possible they won't win.
This is just one possible political system. REsearching a new "Unified High Council" option could potentially allow the Drengin to switch from the ruling council to this other system.
I could help come up with others for each of the other races as well, that are distinctly different from the vanilla Humancentric Senate approach.