While I know Civ 5 and Gal Civ 3 really cant be compared in all game play aspects, one feature I think Gal Civ 3 would benefit from is similar feature to how Civ 5s Brave New World added International Projects, where civilizations in a game are given the chance to all contribute to the same global project effort for benefits. As it is now only the UP chair really benefits or controls the United Planets as they get to choice the proposals. And unless you have a lower player count or high influence you have no real chance to affect change though the UP giving a less then engaging experience.
The project names and effects can be changed but to easier explain things I will call my suggestions the Galactic Projects and Galactic Competitions. These start to become available once the United Planets has begun and a chair has been named.
These are triggered similar to Mega Events, they are rare once per game events. These events give the opportunity for all races to participate regardless if they are in the UP and regardless if they are strong or weak in influence. Allowing them to use their other stronger skills such as Manufacturing, Research or Credit Income as a resource to complete the task.
As with International Projects in civ 5, civs can begin working on Galactic Projects when the event triggers by selecting said project in the production menu in any of their planets. The ability to build it will last until the project is completed. There are three types of prizes that you can get from your contribution to each of these projects, based on the number of the required resource you contributed to the project. Depending on the project event this could require you to use Social Manufacturing, Military Manufacturing, Research, Influence or Credit Income per turn. The first two, ThirdPlace Bronze and SecondPlace Silver, simply require you to contribute a set amount of the Event Resource, while the last one, FirstPlace Gold, requires you to have contributed the most to the project. By giving everyone a more equal footing to participate as well as still gaining a benefit even if you dont win first place makes the whole experience more engaging and gives hard choices on if they can afford to participate. Example being if your In a war or maybe about to start one, you might change your plans to join the project. Or take the opportunity to build up your fleets while your enemies are otherwise distracted by the event.
Galactic Projects Example: https://i.imgur.com/SQ8GrUR.jpg
Deadly Outbreak at [Minor Civ Planet]
Research Project Event
[Gold] Discovered Cure Benefit: Ideology Choice: Most Research Contributed
* +60 Benevolent, +1 Planet [Akia], +1 diplomatic bonus to all other Minor Civilisations. All Akilians ships, star bases and asteroid mines are scraped.
* +60 Pragmatic, High diplomacy bonus and Alliance Treaty with the Akilians, +3 Bonus Trade Routes, +25% to all Trade Routes income. +10% Global income.
* +60 Malevolent , +1 Planet [Akia], Control all the Akilians ships, star bases and asteroid mines.
[Silver] Tier Benefits: 400 Research Contributed
Instant bonus research points based on the total research put into the project by all races.
[Bronze] Tier benefits: 200 Research Contributed
+15% to Global Birth Rate, if synthetic +15% to soldiering.
Unlike Civ 5 however the benefits might also be a hindrance to other races and they also give you Ideology Choice if you are the winner which since it can effect others is the most desirable goal to aim for.
Galactic Competition function on a gameplay level the same as Galactic Projects. With Gold, Silver and Bronze tier goals. The difference being Galactic Competitions are voted on in the UP and if successful the event begins. While the rewards are minor compared to Galactic Projects they can be voted on again and again in order to re-hold the Competition at a later date to be able to get the same benefits.
Galactic Competition Example: https://i.imgur.com/RcDoBZ6.jpg
GALACTIC SPACE RACE
Military Manufacturing Event
[Gold] First Place - Ideology Choice: Most Military Manufacturing Contributed
* +30 Benevolent, +2500 BC, +40% Global Influence for 20 turns.
All participants gain 50% towards their current research tech.
* +30 Pragmatic, +2500 BC, +20% Global Income for 20 turns.
All participants gain 25% towards their current research tech.
* +30 Malevolent +1000 BC, +25% Global Research for 20 turns.
All participants gain 10% Gross income for 10 Turns
[Silver] Participation Award: 500 Military Manufacturing Contributed
1 Free Tiny Scout Ship with high move speed.
[Bronze] Participation Award: 250 Military Manufacturing Contributed
+10% Miniaturization for Engines, or 15% Bonus towards your current research project if you already gained this benefit.
I have alot more ideas for events but they seem superfluous as I really only wanted to give the basic idea of how the events function. As I said the rewards and names are just examples and not balanced. I feel like these ideas would enhance how the United Planets function as it will give a greater chance for participation by all races as well as give the potential to change the dynamics of the universe at any given time keeping mid to late game play fresh and engaging.