I did that for my half yearly and journeys portfolio as well; it's a pretty good text.
Some ideas I extracted from it were (from the top of my head):
- King's 'vision' - how imaginative journeys occur through speculation
- King refers to the past as well as the future eg: the American government's from for civil rights to amfrican americans etc
-imaginative journeys can be personal - king presents his own vision/goal
- it also shows imaginative journeys can be shared - king is sharing his journey to a wider audience - talk about how journeys can be 'layered' - ie: the text encompasses more than one journey.
- look at King's use of oratorical techniques eg: rhetoric, allusion - Gettysburg address etc.
- I did the text only, but if you want to look at the use of tone, pause, pace etc you can do the actual delivery of the speech - it's eaisly found online.
Hope it helps. Good luck.
