Investing in bitcoin is a risk, as the value can crash tomorrow.
I'm holding too so far, I believe in what bitcoin represents, so I'm taking the risk. Don't invest more than what you can afford to lose however, but if you can, you should buy more.
Also have a look in other cryptocurrencies.
There is always a risk in investment. In bitcoin I think holding is okay because at the moment the value is skyrocketing. This could still do up on uptrends. One just have to be patient enough and wise enough when to but and when to sell.