This is a wonderful idea, I would certainly like to visit phased off areas with group members ( ops group as well). There are so many cool little areas on each planet that you can only visit once and then it's done unless you roll another character. It would be great to be able to access these areas regardless of class, quest or even faction restrictions.
I would like to add to this. But here is the Spoiler warning!!! So something that would be nice is to allow cross faction planet travels, even if it's a completely closed off faction instance ( or just make it so you can't attack the guards or NPC's that aren't normally hostile.) It would be nice to plan some RP for a coastal area on Imp side and not be restricted to Rishi, let us go to the wonderful coasts of Ord Mantell, or for Pub players to play around in some tombs on Korriban.
Lastly, ships... No reason we can choose our own once the Class story is over ( really want to cruise around in a Fury on all Imp side toons.)