Even if there were only 50 different memes you could have or not have, that's 2^50 possible combinations, which is 100000 of times the population of the earth.

This is true but that doesn't have much to do with the argument in the original post. Some people think that humans are just the hollow-ware for memes and that the complexity of values and goals is a fact about our culture and environment more than a fact about our neurological settings.

Our evolutionary mind-template might only feature a narrow set of values and goals. Small fluctuations in this template seeded human societies with lumps that eventually grew into complex cultural and academic preferences.

If that is true then humans appear to be unique only due to the rich cultural environment they are embedded in. The apparent complexity of value exhibited by human beings is a result of their upbringing, education, bodily environment and experiences.

If an AI was going to look at how many unique evolutionary templates there are it might come up with a much smaller number than there are people.

If the complexity of value is induced and not an intrinsic property of our genetic make-up then any AI that would attempt to extrapolate our volition by making us more knowledgeable would mainly be extrapolating the inherent consistency of that knowledge as such artificially induced ideas might override any evolutionary values.

I have written more about that here.