All of those things are tied to species size, but I didn't actually say size of the species (if by size you mean their physical size). A smaller animal would typically need less food, smaller housing etc. Although quite right it isn't necessary, you could also want to RP a race that live in extremely close proximity and behave somewhat like an ant colony. It's all about how you want to imagine it, and making an arbitrary "this is the point at which you become overcrowded" restricts that.
Would your suggestion satisfy my complaint? Well, not really. If it was going to be implemented I would prefer it to be implemented without that, based on the original formula. Adding in those sorts of exceptions just complicates things and wouldn't actually alleviate my problem. I am of the stance that such a mechanic should not be added at all, so attempting to add it with some sort of appeasement isn't going to satisfy anyone. From my point of view, either add it as you want it or don't. If it's a popular idea there's no need to add in something to make it appeal to me because it never will.
Yes smaller creatures need less food. You must also remember that each being requires 1) a space for their community, apart from the rest. 2) distance from enemies, or those they may think are enemies.
1) While you may think that a creature can just be an ant, all creatures have a certain amount of space required, with more personal space being required for smarter creatures. Ants are more like human being in the sense of nationalism, but extremely stupid and able to be fit into a denser area together. An intelligent, free thinking alien settler will, no matter how small they are, require an area able to house their own community. Human communities are about 150 people, with smarter beings able to have slightly larger communities. While a small species could easily get by with an acre of land no problem, I bring up number 2.
2) Paranoia is common in all species, especially intelligent ones. If you aren't prepared for your neighbour to invade you, they might take you by surprise. Therefor, most species will prefer to live rural, unless the convenience of urban life outweighs the risks. Modern urban life is made possible because of easy access to non-subsistent jobs (paid jobs), and crime prevention (police). If a community of people get thrown into a sea of unknown communities (or even known), unrest and crime are sure to follow. Remember that a criminal who is anonymous will have little risk in committing crime in an area.
Modern day society is already overcrowded in this way as well, although not evenly over the world. A future society based on TNT (trans-newtonian tech) means that an enemy is a ten minute commute away at all times. While a conventional start would have a high population, TNT would quickly create overcrowding and crime issues, requiring expansion. While your right in saying there's no need for arbitrary overcrowding points, there needs to be overcrowding. It can be done incrementally over time, with higher populations requiring more policing, more luxury and more power. Eventually you would reach a point that you would need population control measures to prevent future unrest. Which leads to point three.
3) All exponential growth is finite, because of the risk of doubling. A population will grow faster than people might think, with a 1% growth rate resulting in your population doubling every 69-72 years (depending on how accurate you want to be). Remembering the chess board experiment in school, a population would eventually explode to the point of the long integer overloading. Using a bigger integer would only deal this problem for another couple of doubling cycles, thus a hard limit must be made. Eventually you'd reach a point where the population will be rising too fast for your colony ships to move them. Your only choice then would be to cull the planet, which should incite revolt and unrest as well.
So I've made two points based on creature size and how it's irrelevant, and one from a gameplay perspective.
Does this "Appease" you?
EDIT NINJA POST BY THEOKRAT!!!
Yes, I know. Resource shortfall is one of the primary reasons of crowding that is understood and quantifiable at both the small and large scale by todays science. What I was trying to say was that just because technology is more advanced in the future, does not mean we will be able to support massive populations. No matter how advanced the social engineering becomes, it all comes down to resources.