Something of value that is worthless in the current context?
Is there a word/metaphor/idiom for something that has value, but is worthless (or even harmful) in the current situation?
To use a couple of monetary examples:
A check for $1,000,000 has potential value, but unless you can get to a bank that value is inaccessible.
A duffel bag full of cash is also extremely valuable, but if you try to hang onto it after being thrown from your speedboat in an explosion, it will drag you to the bottom of the Long Island Sound.
The metaphoric gist I'm getting from your question is :
"the cure is worse than the disease"
"don't throw water on a grease fire" and the related "douse the embers in gasoline"
an environmentalist friend of mine once said "they're still solving their problems with cane toads and kudzu" which made me laugh and seems totally appropriate. These were invasive species that were originally brought in to solve smaller problems than the one's they created.
A number of writers have used the image of a golden millstone to describe something of great value that becomes a great burden. Here are three early examples. From "Prof. Norton's Dante," in The Critic (January 23, 1892):
The wand of Dante points to this and that mystic canvas, while the poet explains in exquisite musical cantos one after the other of the great circles of pictures that pass before him in the triple allegory. He is one of those men to whom one becomes attached in youth and remains attached until old age,—a sort of golden millstone hung round one's neck, a haunting presence that will not be allayed.
From Oliver Herford, "The Miser Elf," in St. Nicholas (September 1894):
But, ah! with all his golden dust and jewels rich and rare,
This little elf was never free from misery and care.
The wealth that might have conjured up all good things at his beck
Was just a golden millstone that hung around his neck.
He never had one moment's peace, his treasure out of sight,
Though he buried it for safety in a different place each night;
Each night the thought of robbers made him close his eyes in vain,
And just as soon as it was light, he'd dig it up again.
From Marie Corelli, The Treasure of Heaven (1925):
Death, however, in its fiercest shape, had now put an abrupt end to any such benevolent scheme, whether or not it might have been feasible,—and absorbed in a kind of lethargic reverie, he again and again asked himself what use he was in the world—what could he do with the brief remaining portion of his life?—and how he could dispose, to his own satisfaction, of the vast wealth which, like a huge golden mill-stone, hung round his neck, dragging him down to the grave?
The closest phrase is probably "double-edged sword", indicating that the value is dependent on the circumstance. However, the phrase does not exactly coincide with the concept you are trying to express, because money is good in the vast majority of circumstances, while a double-edged sword implies equal benefit and harm. The adjectives "agathokakological" and "bittersweet" have similar denotations. The colloquial expression "One man's trash is another man's treasure" (indicating that something worthless in one context is valuable in another) could be reversed, forming the anti-proverb "One man's treasure is another man's trash". Additionally, the term "Midas Touch" could be reinterpreted as something that seems valuable prima facie, but in certain circumstances is deleterious (as when King Midas accidentally turned his daughter to gold). Unfortunately, there does not seem to be a word that perfectly matches that concept. I hope these related terms can be adequately substituted.