You're making a giant number of implicit ill-founded assumptions here that must all be true. Read my section on the AI space in general.

Firstly, you assume that the 'stuff' is unbounded. Needs not be true. I for one thing want to figure out how universe works, out of pure curiosity. That may likely be a very bounded goal right here. I also like to watch nature, or things like mandelbox fractal, which is unbounded but also preserves the nature. Those are valid examples of goals. The AI crowd, when warned not to anthropomorphize, switches to animalomorphization, or worse yet, bacteriomorphization where the AI is just a smarter gray goo, doing the goo thing intelligently. No. The human goal system can be the lower bound on the complexity of the goal system of super human AI. edit: and on top of that, all the lower biological imperatives like desire to reproduce sexually, we tend to satisfy in very unintended ways, from porn to birth control. If i were an upload i would get rid of much of those distracting nonsense goals.

Secondly, you assume that achieving of 'stuff' is raw resource-bound, rather than e.g. structuring the resources - bound. So that we'll be worth less than the atoms we are made of. Which needs never happen.

In this you have a sub-assumption that the AI can only do stuff the gray goo way, and won't ever discover anything cleverer (like quantum computing, which grows much more rapidly with size) which it would e.g. want to keep crammed together because of light speed lag. The "ai is going to eat us all" is just another of those priveledged baseless guesses what an entity way smarter than you would do. The near-FAI is the only thing with which we are pretty sure it won't leave us alone.