word choice - What's the difference between せっかく and わざわざ?

せっかく and わざわざ seem to be pretty close in meaning/usage, but is there ever a time you would use one and not the other? Or is there a small nuance there?

Just to give some example sentences:

「せっかく来てくれたから、昼ごはん奢るよ。」

「わざわざ美容院に行ったのに、雨で髪がくしゃくしゃになっちゃった。」