This is how I imagine the general form of utilitarianism's utility function: assign all states of being a quantity of fun, which can be positive or negative. Multiply all fun-values times the amount of time over which they are being experienced times the number of beings experiencing them.
This utility function could be optimized by bringing people into the universe when the total fun-impact that they would have on the universe (including themselves) is higher than would be the total fun-impact of not bringing them into the universe.
However, this utility function only cares about people's preferences if they either already exist or may be brought into existence. It could act on data which suggested that sentiences with certain preferences were more likely to exist than sentiences with other preferences, but I don't know if we have any strong data in that area. (I would suppose not, but I don't think I've thought about it long enough to make a positive claim.)
As to why I'm discussing utilitarianism: all utility functions which assign utility to the fulfillment of others' preferences is a form of utilitarianism -- if you object to valuing all sentiences equally, then add a multiplier in front of each sentience indicating how much you value fun it has over that which other sentiences have. Either way, I think that the above conclusions still apply.
Some people see never-existed people as moral agents, and claim that we can talk about their preferences. Generally this means their personal preference in existing versus non-existing. Formulations such "it is better for someone to have existed than not" reflect this way of thinking.
But if the preferences of never-existed are relevant, then their non-personal perferences are also relevant. Do they perfer a blue world or a pink one? Would they want us to change our political systems? Would they want us to not bring into existence some never-existent people they don't like?
It seems that those who are advocating bringing never-existent people into being in order to satisfy those people's preferences should be focusing their attention on their non-personal preferences instead. After all, we can only bring into being so many trillions of trillions of trillions; but there is no theoretical limit to the number of never-existent people whose non-personal preferences we can satisfy. Just get some reasonable measure across the preferences of never-existent people, and see if there's anything that sticks out from the mass.