If you understand why it's valuable i'd say go for it.
If you're picking one up to hold onto for a while buying a couple is ok but if you're serious about investing i'd dollar cost average and but a few dollars worth each week.
Really comes down to where you think bitcoin is going to be down the road. The price to me stopped being anything but a number that people keep reminding me when the topic comes up some time ago. I have no idea where the price is going but i definately believe the market is easily manipulated since its so illiquid so to me any price is a good buy price when the asset you're coming from is worthless imho.