Bored?

well there are many factors involved with morale, part of the reason you're getting that are simply the side effects of overcrowding such as pollution, crime, very little living space (although I'm sure the Yor wouldn't mind small cubicles to 'sleep' in), etc. Although its represented by a single factor or a few factors, not sure on the exact mechanics.

also, what population size are you seeing this decrease in morale no matter how many 'happy sites' you put up? there is a point where this normally happens.

20 billion is the limit - morale drops exponentially from that point on up to 25 billion. Upwards of 25 billion has no increasing morale defecit - however by the time you finish building all the necissary farms and multimedia centres to get that far, you would have been far better off sticking with 20 billion and build stock markets.

Actually you're better off with 12B and stock markets if your criteria is the economy.

how happy are you standing in line to see a sporting event or concert and every year that line gets longer

so it is reasonable that the higher the pop the less effect of the happy sites

the standard maximum population for one farm is 13 bilion except on homeworlds. 13 billion, one farm and one multimedia centre is the most efficient economic model, however in order to take advantage of this efficiency you would need to increase taxation which causes problems for developing worlds.

I find i can get a much easier balance with 20 billion and be able to keep taxation fairly low - 33% to help developing planets grow quicker. Also having more population for my transports is nice too!

Does that stop people from going to the Super Bowl? In relative size, each "Square" is larger than the North East United States, meaning that's a lot of s*** to do; and when 1/6 of the planetary tiles are spotted with em, I don't want to here any bulls*** about them getting bored.
It's simply an effect of time from what I've observed. In 2226 I could build a VRM that provides 60% entertainment on a 10B Pop world, then see that same VRM provide only 20% on a 6B Pop world.
So if I hear any crap about them simply becoming less entertaining, I'll point you to the numerous tourist atractions and year-round crap states and nations run that simply become more ardous and traffic-blocking, but still fun to watch, each year.

Cram people together like sardines, and they'll manage, but they aren't going to be happy about it.

there is no point in arguing about the logic of morale in the game compared to real life.

first of all in real life, morale effects population growth in quite the oposite fashion as to in the game. Overcrowding does not impact morale all that much in real life since it is somthing people have grown up with and are used too.