In which I yield the floor to SteveD, who has been writing RPGnet's Campaign Toybox for almost two years now, firing off game ideas at a fair old clip.
And inevitably, some of them could make great Doctor Who adventures due to the bigness of its kitchen sink setting. There are two different time travel campaigns in there, for starters, as well as Twenty Six New Ways to Travel In Space.
And going all the way back to the start, 70s cops dealing with a Stargate at Stonehenge. Put poor old underfunded UNIT on the job and that's a Pertwee-era series idea.