Eliezer has anticipated your argument:
"Um - okay, look, putting aside the obvious objection that any sufficiently powerful intelligence will be able to model itself -"
Lob's Sentence contains an exact recipe for a copy of itself, including the recipe for the recipe; it has a perfect self-model. Does that make it sentient?
I think it's relevant that the self-model for an AI would change as the AI changes.
In the novel Life Artificial I use the following assumptions regarding the creation and employment of AI personalities.
(Note: PDA := AI, Sticky := human)
The second fitness gradient is based on economics and social considerations: can an AI actually earn a living? Otherwise it gets turned off.
As a result of following this line of thinking, it seems obvious that after the initial novelty wears off, AIs will be terribly mistreated (anthropomorphizing, yeah).
It would be very forward-thinking to begin to engineer barriers to such mistreatment, like a PETA for AIs. It is interesting that such an organization already exists, at least on the Internet: ASPCR