I think that not only do you add a few new planets, but expand greatly on them, and the places to go, anywhere, like a gta type anywhere. That in itself would add tons of more excitement of exploring.
Also, why do people want to add so many sith related worlds? From the past two games, the sith worlds seemed kinda empty. Planets like Mustafar and Hoth are way to unihabited to have anything of real interest on it.
I agree that Corusaunt should be added (with maybe your own speeder to drive around with ), and Corellia does sound good to add, and Alderraan as well.