Saving will make your money grow soo slow that you will sleep watching it .With investment you wont be able to sleep well,as you will imagine if you making money or loosing it,the thing is investment will always be better as the potencial return.
Its depend on fiat money now, because buyers of bitcoins or users are depending on the price of bitcoin, they will used it, buy or sell bitcoin when they know if the price of bitcoin is high or low, So its means bitcoin is depending on fiat money presently. In future Bitcoin will be widely accepted money So people should try to adopt it more to make growth in bitcoins.