Phew, I'm relieved your argument isn't something like "a simulation would by assumption be 'grainier' than a natural universe, and so it would 'split' less often, and so have less 'subjective experience.'"

As to it being a gigantic pain in the ass to simulate an entire universe - sure, and it's unlikely that we're in a simulation. But ignoring units is typically only done when even the exponent is huge, since 10^10^10 meters is 10^(10^10 - 3) kilometers, which is still pretty much 10^10^10. On the other hand, it should only take some well-designed nanotech to keep things running, which is a factor of 10^20 at the worst, which isn't a huge exponent. It's certainly more than we have in our universe, but it's well within what we could have if we had a few extra spatial dimensions or a different history of our vacuum energy or something.