One is the principle that the utility function is not up for grabs,

I don't buy this. Many people have inconsistent intuitions regarding aggregation, as with population ethics. Someone with such inconsistent preferences doesn't have a utility function to preserve.

Also note that a bounded utility function can allot some of the potential utility under the bound to producing an infinite amount of stuff, and that as a matter of psychological fact the human emotional response to stimuli can't scale indefinitely with bigger numbers.

And, of course, allowing unbounded growth of utility with some tilable physical process means that process can dominate the utility of any non-aggregative goods, e.g. the existence of at least some instantiations of art or knowledge, or overall properties of the world like ratios of very good to lives just barely worth living/creating (although you might claim that the value of the last scales with population size, many wouldn't characterize it that way).

Bounded utility functions seem to come much closer to letting you represent actual human concerns, or to represent more of them, in my view.