The price of the bitcoin is unstable, a month can go up to 50% but could drop by up to 50%, it is very risky for the corruptor to save money because there is no money opportunities bitcoin runs out.
Funny you consider this as an issue for the corruptor, although this not seems to be a big problem for them. As long as they store and keep their bitcoin no matter how low the price of bitcoin at the moment, they can still wait for it to increase. I think the biggest reason of them using bitcoin is that to hide their corrupted money so that they will not easily get caught.
We must remember that the bitcoin fluctuations are still balanced even though they are often up and down, we can see the current bitcoin prices, and if viewed from corruption, this is not a big deal because the most important thing for them is by Washing their money as much as possible, depreciation is inevitable , Bitcoin is not money that can be lost and this is the entrance to speculate from corruptors.
No don't just disregard bitcoin as money, because if it's not a money why isn't you spend it to buy what you liked to spend on some goods. In fact more people were now using bitcoin as their mode of payment system online, particularly those digital currency users. Although speculations were normally happening in the market, it's not assurance of no corruption with bitcoin; but if those hidden transactions made of corrupt people which their bridge is through bitcoin. I think that is beyond our control and yet bitcoin is having it's own freedom of any transactions, as long as requirements is completely complied.