This morning I was talking about this with a buddy of mine.
Right now we have miners all over the world trying to solve this exponentially hard algorithm to earn their bitcoins. That is their incentive and that is what drives them to do so.
What happens when we remove that incentive to "mine" aka "verify transactions" on the blockchain? What I'm basically asking is what happens when we hit 21,000,000 bitcoins from the perspective of the miners?
The law of demand and supply will answer your question in terms of the price. Assuming that every bitcoin is already mined, the supply now will be limited to the ones holding bitcoin and the person who has the most bitcoins might have the potential to control the price depending on his supply. Due to all of these factors, the price of bitcoins would significantly increase on the market and investing it would be the right choice. Though one disadvantage that it might result is the number of campaign signatures might decrease, or rather use another type of cryptocurrency as for their payment; but then again this is all speculation.