Do you make a love letter to the fans of the series as a WHOLE, or make it more about the show as it is now?
No question you make it a love letter to fans of the series as a whole, since we're celebrating the 50th anniversary of the premiere of the original show in 1963. If you want to just center on the new series, you'd only have to wait a couple more years for the 10th anniversary of the premiere of the Christopher Eccleston series in 2005.
Personally, I think more should be done to educate the new fans on the show's rich history. Whenever I see any of these new retrospective specials on BBC America, I get frustrated that they mostly seem to be pedantic rehashes of the plots of episodes that most fans already know. Now, I suppose the real purpose of these specials is to educate the super-new fans who've never seen anything before. But still, I think specials like that would be a good way of giving new-series fans a good overview of the classic series; particularly for the new fans who don't have the patience to sit through the glacial pacing of most of the classic series.