First of all, a great big to mqpiffle for making this thread. What a fantastic idea! Now, on to the UI things I agree most with.
Quickslots for strategic spells [Azunai_]
I intensely dislike having to flip through my spellbook repeatedly to buff units, especially. It's not so much of a problem when I want to cast enchantments on cities (they are on the first page of the spellbook and in plain view most of the time), but when I want to buff an army group for a tough battle, I don't like having to open it up and cast once for each stupid unit in the stack.
A shortcut dedicated to moving through idle cities only [jonmdewey]
The reason I agree with this should be rather straightforward. This is useful, especially when you reach a large number of cities.
Option to remove enchantments on a unit from within the unit's Unit Details screen [Azunai_]
Dispelling enchantments is currently too difficult. You can see the little icons in the unit's display in battle detailing what enchantments they have (I think) but for some reason to dispel one on the overhead map you have to go the Ledger and manually dispel it from there. What a chore!
Cutscenes...lots of cutscenes. [GFireflyE]
I really like the cutscenes that happen when you start the game, or when you find a wildland, and all of those. They have beautiful art, and really help with game immersion. I understand that this one is a bit wishful, though, considering how much extra work would have to go into the art and design of said cutscenes. Nonetheless, it is a HUGE benefit to immersion and interest levels and I really think the game would benefit from more.
Allow the player the options to delete and edit sovereigns and factions on the sovereign/faction creation screens, instead of having to go to the xml files. [Borg999]
Yes! I built some really dumb factions that are just plain bad when I started playing this game and I haven't a clue how to delete them, so the AI is stuck with horrible factions that don't even have a good custom unit pool to draw on. Seems a bit unfair.
+2 Allow use of any resources to negotiate for treaties (Why are trade and treaties separated in the first place?)
This makes no sense. We need to fix this. Diplomacy is hard enough as it is, why won't the AI accept horses and stuff for treaties, but they'll accept them for trades? Treaties have a diplomatic value, and one that should be matchable by resources too.
Allow for two faction colors on the ZoC, one for the base line and another for the particle glow above it. This would alleviate a lot of UI issues, especially with many factions in a single game.
There is a clear need for this. I inadvertently made two of my factions have the same main faction color and they spawned next to each other... needless to say, way too much confusion arose.
There are probably a lot of things I've thought of while playing the game myself, but I can't think of them at the moment.
I do hope more members read and give feedback on this thread! I think it will really help out the people at SD if they know what kind of UI changes we want.