First and foremost, this is a game. I only need enough realism so I'm not constantly suspending my disbelief just to play. If we're in the year 2017 and we're still using hit points to determine whether a ship is "dead" or not, then I think I can handle whatever population model I'm given.
One thing we need not to do is swing the pendulum back to how it was in Galciv1. Back then, planet class and population meant too much, and only the class 12's and up mattered. A lot of what we're seeing is to make sure we don't go back to that again. I *DO* like in Galciv1 how new colonies were actually a drain on your economy until you got the new planet up on their feet. The problem was that class 4's never made you back your investment. Class 4's need to be valuable, but for different reasons than for class 16's. Therein lies the reason why I think population should scale linearly for money and influence, but not for other things. The class 4 has proximity to asteroids (which is reason enough in my book), mining, unique research opportunity, tourism, or military advantage. And still, 4 population is less valuable than 16, but still better than none at all. A class 4 has value as an outpost. A class 16 is a population, financial, governing center.
There is also this artificial marriage which says that high-class planets have to be these wonderful, population-attracting places, while class 4 is some crappy Mars place; you might as well be living on a starbase. Not so. Planet class is the size of the planet, in terms of buildable tiles. You can have a crappy, large Dune world, with a paradise moon around it where the population is incredibly dense. A class-4 planet, with two adjacent Paradise tiles and one Planetfall tile. And population is what it does.
