I wouldn't say its not of value. Theres plenty of coins you can mine with a GPU that don't have all too much value right now, but can grow exponentially. Like everything, its risk vs reward. You could end up making a ton if the price skyrockets for the particular coin you mine, or it could be worthless and you might end up spending more in electricity and the cost of the GPU(and GPU wear if you were planning on using it for gaming in the future).