Well the OT period has had its fair share of expanding.... The "Tales" books and comics are an *excellent* place to start. You get to find out everything about everyone in the cantina scene, or in Jabbas Palace, or the Bounty Hunters summoned by Vader in ESB
If you want an extra kick, check out the Radio Dramas....they are just plain awesome, and for EU fans, excited about extra bits there's *heaps* of extra material, scripted by Brian Daley and approved by GL himself. To put it simply, it takes the 6 hours or so of movie material and extends it into nearly 14 hours!!
of engaging audio drama, with fantastic production values.
Alot of people simply dont know or have forgotten about the radio dramas... Check em Out !
so, to answer your question Jo, the OT has been expanded plenty I say.
I personally want to know :
*What happens between 3 and 4
*The Rise of the sith Lords post Darth Bane and ending in Plagueis/Sidious
*Post NJO and beyond
*More KOTOR era stuff
*More about Yoda and his time as a padawan and young jedi knight
Most of these things are going to be covered in upcoming books and the TV shows...cant wait !