OP here. I too took this as a buying opportunity. $400 interestingly was a low hit around April as well. There's no rhyme nor reason to my buying other than an intuition about what "low" may mean. For me its a long term hold. If the price fell to $350 I would still hold. In fact if the price fell to $200 I would probably hold unless the whole Bitcoin system was somehow compromised and it was obviously going to $0...
That's my biggest problem with bitcoin. If someone figures out how to reverse sha256 they could just mine blocks here and there without attracting too much attention, but in reality the whole thing would be on shaky ground and truly worthless.