Why is life valuable? Because we have a finite amount of time. To live life is to spend time, and the fact that our lives are time-limited is what makes them so valuable and so priceless.
What about an eternal afterlife? Is there any value to it? In an eternal afterlife, you have an unlimited amount of time. You don’t even have a million years, or a billion years, or a googolplex of years; you have an infinite, non-numeric amount of time. You cannot quantify the time available in an eternal afterlife other than to say you have an "infinite" amount.
Of what value is something when you have an infinite amount of it? To expand on this question, let's use an analogy (I love analogies). Let's use a "Bill Gates" analogy. Bill Gates will represent a soul in an eternal afterlife, and Mr. Gates' money will represent time.
Now in this world, Bill Gates is the richest man in the world. But even then, his money is finite. It can be quantified in a specific number. For example, Bill Gates can have 99999 trillion dollars and could still earn more money. He can still add to that total. But what if Bill Gates had an infinite amount of money, with no numerical quantification possible? He would not be able to add any money to an infinite total. Bill Gates, with an infinite amount of money, could spend and spend and spend all day long and still have an infinite amount of money. There would be no point in him working for cash, as he would not be able to add to the total amount of money he had, since the amount would already be infinite. The money would lose value to Bill Gates because no matter what he did, he would not be able to get rid of it. Eventually, Mr. Gates could literally buy everything. He could purchase every material possession, he could pay for every conceivable service, to the point where he would have everything and there would be no further use of his money. In time, his infinite amount of money would become worthless.
Now let's apply this to the afterlife. In an eternal afterlife, your time is infinite. You would not be able to get rid of any of it. You would have an unlimited amount of time to do anything and everything. In an infinite, eternal afterlife, eventually you would do everything that could be done. You could eventually run out of things to do or accomplish, but you would never run out of time with which to do it in. Your eternity would, like Bill Gates infinite money, become worthless.
Even a technological immortality (of which I champion in previous posts) would not be like having an infinite eternal life (or afterlife). For a technological immortality would still have risk or finiteness associated with it. The technology wouldn't last forever without care or maintenance. Steps would have to be taken to prolong one's life, but having a guaranteed eternity of life would simply not be the case with a technological immortality. A technological immortality, at best, would simply provide the option of continued life provided that one has the resources, time, and energy to maintain this immortality.
But an eternal afterlife would not have any risk associated with it. No attention need be spent in maintaining this eternal property. An eternal afterlife would not grant time provided that one maintains or spends attention on devices that grant this time, as in a technological immortality. But instead, an eternal afterlife would grant unlimited time immediately, consistently, and without any energy or time spent on obtaining this eternal time.
What other things are found in the afterlife in unlimited, infinite amounts? Learning? Accomplishment? Goal reaching? Can there be an infinite amount of things to learn and goals to reach? I don't think that there can be an eternal amount of goals to reach in an eternal afterlife. Some might say that eternal happiness can be found in the afterlife. Happiness for what? Happiness is caused, and what can cause an eternal happiness? Money in itself doesn't make one happy, as any rich person will tell you. So why should simply being in an eternal existence make one happy? Maybe God would be the cause of the eternal happiness, but then that would be an artificial external happiness forced upon you, rather than being a happiness that comes from within. And in an eternal afterlife, even happiness would get boring.
How about the concept of eternal boredom? Boredom comes from being static, from a lack of stimulation, from a lack of new material to process. Even a person's favorite ice cream flavor gets boring if it's all they eat. Because an eternal afterlife would have infinite time, things would ultimately be static, or they would at least feel static. Everything that could be done would be done an infinite number of times in an eternal afterlife. The static feel of an eternal afterlife would cause eternal boredom. It would bring a feeling of eternal non-stimulation and eternal over-exposure to everything one could experience.
This is starting to sound a lot like eternal torment if you ask me! Eternal afterlife? No thanks! Quality is more important that quantity. I'll just stick with my finite, valuable, priceless time.