I'm going to Iceland this December with the hopes of catching the Northern Lights. We were considering doing a tour, but we were considering renting a car and drive around hunting for them ourselves. Potentially we could follow some of the buses too.
The main reason is, we have enough people to fill a car, so it would likely be cheaper than going on a tour bus. And also it gives us more flexibility, i.e. we can choose when to go and when to leave.
However, I'm unsure if this is possible, and how hard is it to look for the Northern Lights? Is it as easy as driving out far from the city? Are the tours worth it? Have people had problems where, the tours end too early?