the upper limit is 25billion, this was explained elsewhere, but i think i remember it. the - morale from 25b peopl is -60% the morale building only help a little.
25% increase will reduce the -% by 15%. So, in other words, on a planet with less than 15 billion people, (the other morale point) and no morale centers, you will get on your planet with more than 25billion -60% morale. Lets say the planet with 10billion people has 75% morale, you would then have 45% morale on the planet with more than 25 billion. If you had 4 VR centers (on the heavily populated planet) , and no happiness resources, you would have 75% on the planet with more than 25 bil. This works in our favor, bc if we had a planet with 500 billion people, it would have the same - morale as the 25 billion planet.
so in other words, now that i have bored you all to tears, build lots of happiness resources, vr centers, and stock exchanges. They all give morale. In all my games i have never had an issue with economy, in fact, i usually have huge production backing that economy. no fleet to 8000 fleet rating in 1 turn.
In most of my games, unless i find a class 20 or above with precursor mines or libraries, i turn them into pop centers. Lots of morale centers and farms. and stock exchanges. Most planets below 20 in my games become secondary reasearch and production centers.