Lorne Rosson has an interesting post about Doctor Who, discussing how the protagonist's actions over the years (i.e. the various "doctors") have effected political change. The idea is that the Doctor has generally left things alone with the alien cultures he visited, yet, at times, he has managed to encourage revolution and foment a political shift.
On a personal level, I am grateful for Russell T. Davies and Phil Collinson's revival of the TV series. I am a huge fan of David Tennant's rendition of the Doctor.