If you follow the general rule of thumb with investments, one would think that it would not be a good time to buy because the value seems to be up (which means it will come back down at some point). However, when it comes to a new currency like Bitcoins, it's hard to tell where the drop off will be. 6 months ago I bought one on a fluke just to have one. I paid $100......its value is now floating around $1,000. That's a 1,000% increase in value, which is pretty incredible. Also, something else to consider, big companies are just now beginning to accept them as payment for goods and services (plane tickets being the most recent, and I think I heard about a car dealership selling a Tesla for them as well).
In summation, I would advise you to buy if you can spare the money. I think that as they become more accepted and more popular, the value will continue to increase until it's a more commonly used currency. At that point, the value will most likely just level out and shouldn't drop back down too far.