I think you make a nice point. Since the goals of our future selves tend to be similar to our own, we should care about our future selves ability to accomplish their (and by extension our own) goals. However, I see two potential problems with this argument.
1) A large part of our investment into the future is concerned with general well being rather than with abstract goals. For instance, the fate of most intellectual endeavors (publishing a book, making a scientific discovery etc) is usually determined long before the age 65. Still most educated people try to save money for a comfortable retirement.
2) If the life is transient it seems hard to motivate any goals which are not immediately related to our present well being. Naturally our present well being depends on our ability to believe in existence of such goals. However, fooling oneself into believing something false seems like a classic example of “irrationality”.
1) Isn't general well-being a precondition for many of our other goals, and one that we know we will value in and of itself about as highly in retirement as we do now? The aspect of ourselves that is concerned with general well-being is probably one of the most invariant, so I can be sure with very high probability that all of my future selves will value it highly. Perhaps I'm not understanding your point here, but it seems to me that though I will be different in 30 years, I will still (justifiably) perceive myself as the same person, so I should care now...
From the dawn of civilization humans believed in eternal life. The flesh may rot, but the soul will be reborn. To save the soul from the potential adverse living conditions (e.g. hell), the body, being the transient and thus the less important part, was expected to make sacrifices. To accumulate the best possible karma, pleasures of the flesh had to be given up or at least heavily curtailed.
Naturally the wisdom of this trade-off was questioned by many skeptical minds. The idea of reincarnation may have a strong appeal to imagination, but in absence of any credible evidence the Occam’s razor mercilessly cuts it into pieces. Instead of sacrificing for the sake of the future incarnations, a rationalist should live for the present. But does he really?
Consider the “incarnations” of the same person at different ages. Upon reaching the age of self-awareness, the earlier “incarnations” start making sacrifices for the benefit of the later ones. Dreams of becoming an astronaut at 25 may prompt a child of nine to exercise or study instead of playing. Upon reaching the age of 25, the same child may take a job at the bank and start saving for the potential retirement. Of course, legally all these “incarnations” are just the same person. But beyond jurisprudence, what is it that makes you who you are at the age of nine, twenty five or seventy?
Over the years your body, tastes, goals and the whole worldview are likely to undergo dramatic change. The single thing which remains essentially constant through your entire life is your DNA sequence. Through natural selection, evolution has ensured that we preferentially empathize with those whose DNA sequence is most similar to our own, i.e. our children, siblings and, most importantly, ourselves. But, instinct excepted, is there a reason why a rational self-conscious being must obey a program implanted in us by the unconscious force of evolution? If you identify more with your mind (personality/views/goals/…) than with the DNA sequence, why should you care more for someone who, living many years from now will resemble you less than some actual people living today?
P.S. I am aware that the meaning of “self” was debated by philosophers for many years, but I am really curious about the personal answers of “ordinary” rationalists to this question.