Jikan:
What's the difference between Amida's enlightened nature and the practitioner's enlightened nature?
I don't believe there is a difference; that is why Tariki works.
You find it in the sutras, the Pure Land is all about the Dharma, teaching is happening all the time everywhere. Even the wind, blowing through the leaves of the Bodhi-tree, when heard by beings everywhere, gives them insight into the dharmas and they attain the stage of non-regression. Also, even before being born there, the initial motive, shinjin, is for the attainment of buddhahood and not about being born into a heavenly realm.
You might be right. Maybe it's just a pet-peeve of mine. The literal description of the Pure Land just seems too gaudy for my taste (maybe I should try for rebirth in a different Pure Land

) I have very epicurean sensibilities --as in the actual philosophy of Epicurus, not the popular definition of the word. I appreciate wholesome food and simple, unadorned beauty, but hedonism and luxury repel me. If I were going to strive for nirvana, I would choose to do it in an environment that resembled a monastery, not a vacation resort. But perhaps those descriptions that put me off were intended to lure individuals with more luxurious tastes into seeking rebirth in the Pure Land.
You agree that nirvana is eternal. Buddhas are always "in nirvana" and there's no time limit in buddhahood. A buddha-land is a creation, an extension of a buddha. How couldn't it be eternal? Still, it is not eternal in the sense of constant but that its continuity has no end.
Since I don't know how a buddha-land could be created, it's a hard question to answer. Nirvana, as I understand it, is achieved by extinguishing evil passion, seeing through delusions, and severering the bonds of karma once and for all. It's a changeless state of existence. Buddhas themselves may exist in bodies, which aren't eternal, or as a state of pure, diembodied consciousness; but the achievement of buddhahood is, in any case, eternal.
But a buddha-land, I presume, must be a world (a planet, in modern language) ruled over by a Buddha. Planets that support life need to orbit a star, and all stars eventually burn out or go nova, which would kill every living thing living on the planet. Therefore, no buddha-land could be eternal. I'm a pretty open minded person, but I just can't accept something that seems to contradict well verified facts concerning cosmology. I'm not a strict materialist (I believe in spirits, the soul, and I have experienced psychic phenomena first hand), but I do believe that physical things exist and that they are ruled by physical laws which can't be violated.
However, if the Pure Land is a non-physical realm where departed souls exist in some sort of relationship with Amida Buddha, then I see no reason why it should not be eternal. Perhaps the Pure Land exists in what is known as
Arupaloka (formless realm). This way, it would be ontologically distinct from nirvana, though it would still not resemble the literal description in the sutras. Another possibility that occurs to me is that it could be something like a dream realm, resembling a physical realm, but actually a creation of the mind.
I guess it's worthless to speculate on something we just have no chance whatsoever of examining, but it is nevertheless interesting to think about. If there is a Pure Land, we will just have to wait until we get there before we understand what it is.