Bitcoin is not for everyone. It is extremely volatile and very speculative. Arguably, the trend towards higher prices will continue, but at some point there will be a crash. I think the crash -- the big one -- is a long way off, though. Diversification is key.
Yes, diversification is the key within the world of cryptocurrency and without (meaning invest money with other type of investment vehicles). There is no question that cryptocurrency will be a fixture in the future and it would continue on evolving according to the needs of the market. Just like the old saying goes: Don't put your eggs in just one basket! Investing can be a very complicated matter though the rewards can likewise be great and definitely cryptocurrency as an investment is not for all people -- and in life not one thing can be good for all people and this alone makes the world and life go round and round and more excitement.