After that last, rather hastily written post (I've been swamped with work lately), I realized I should have read the SEP article on Parfit's repugnant conclusion before blogging about it. The provenance of the repugnant conclusion is different from what I'd expected: Parfit was apparently led to it by the puzzle of what it means to call a state of the universe better or worse than another if they have different people in them. (This is called the non-identity problem: not related to Quine's maxim "no entity without identity," which a rudimentary acquaintance with Actual People will discredit.) One could argue that two worlds with different sets of people in them are simply incommensurate -- this is one of the ways around the repugnant conclusion -- because "it would be better" is meaningless except as "it would be better for X," where X is a specified actual entity. I'm somewhat sympathetic to this dodge, but it seems overly strong because as phrased it doesn't allow quantifiers. (It's clearly sensible to state that nuking Dresden in 2045 would be bad for anybody living in Dresden in 2045.)
The situation is a little different for the intertemporal version of Parfit's paradox: here, one's measuring the same person's utility at different times. The form of the paradox is identical, however: you have a 50-year high-quality lifespan, ceteris paribus it's good to add 25 years of acceptable but unstellar life, it can't be bad if you even out your quality of life over the 75-year lifespan, rinse wash repeat. One could argue that my self at 50 is different from my self now and I'm within my rights to be a total asshole to my future self -- in which case the good-for-whom point still works -- but I don't buy it. That said, regret is an odd business: gratifications delayed are often gratifications forgone; gratifications indulged lead to syphilis. And it might be true that different parts of one's life are more different from one another than the lives of two different people of the same age, though I wouldn't really buy that either.
Of the eight responses that the SEP offers to the mere addition paradox, about half -- average utilitarianism, steplike or branched utility functions, and the claim that there are no lives remotely worth living -- work pretty much identically in the temporal context. The claim that no lives are worth living is, in fact, on safer ground in this version because it's less susceptible to objections of the happy-space-alien variety. The dumb response, viz. that transitivity doesn't hold, remains dumb. The responses denying that it makes sense to compare two worlds with different people, however, are unintelligible in this context; one is led to believe that they were never particularly good dodges, though some of them might be useful for other purposes. It might be that other dodges along similar lines can be found, but I'm dubious.