Here's one I'm sure everyone will hate for various reasons - ruins "immersion", difficult for the AI to use etc etc - but, off the top of my head:
Precursor Intelligence Planet: A planet that can be communicated with by a Player via Techs (Races find it deep down in the Colonization Tree, but it takes A. Long. Time to research it). I considered making this Precursor Intelligence Communication an Ability, but it's a bit ridiculous having an Ability you might not get to use if there's no Planet of this type to be found.
Essentially: Once you colonize a Precursor Intelligence Planet, and have/get the Tech (which you have to research first, like with you do before colonizing Extreme Planets), you can tell the PIP to prioritise Wealth, Ship Production etc etc and it increases the output available in that field by a factor of it's PQ (ie a PQ4 Precursor Intellgence Planet gives a particular Area a 4 X boost that you can use to say, finish research, finish your planetary upgrades elsewhere, quick-build your New Battlecruiser, etc). And you don't ever have to worry about producing buildings on it, finding resources to upgrade this thing, improve that thing on it. Economic Starbases? Use them for one of your lesser planets. Citizens can go to another planet. Leave your PIP to itself.
There could be two drawbacks to stop it being OP:
1 What I said about not worrying about building improvements? You can't build on the Planet. So the planet's Ability to withstand Culture Flip and Invasion is non-existent. The only way to defend it is a ring of super Military Starbases or big military ships guarding it. Best have your bcs to quickbuild/very good production infrastructure available before you colonize it.
2 Everytime it's Precursor Power is used, it has a cooldown period of a period four times it's PQ - so, the PQ 4 Precursor Intelligence Planet gives a Huge Boost to Wealth of 4, then sleeps for 16 Turns. You'd maybe want to make the cooldown period longer/shorter to balance with galaxy size, number of planets etc in any given game. A "More planets = more chance of finding a Precursor Intelligence Planet = longer downtime period" type of balancing.
Just another idea that I think would help Tall Empires thrive.
TL;DR: Citizens increase a certain specialization by a Percentage forever if you want them to. This is a Planet that increases a specialization by the Factor of it's PQ once every certain number of turns.