Can't believe such a good idea never got any attention from the Dev's.
Someone mentioned EQ2 and even though I never played it, I was told it's profession based levelling (as opposed to this skill based) made it very similar to Star Wars Galaxies MMO. I used the play SWG during the Pre-CU era and I would visit and revisit many of the planets.
This included pure exploration, random missions taken from terminals, doing theme parks with good rewards or taking on World Boss type enemies such as a Krayt dragon in groups etc.
The best thing about that MMO was even though the play area might have been smaller, it was truly open (unlike the on-rails movement we have here) which allowed for player houses and towns/cities etc ... which lead to even more interaction and travelling to and from planets. Also players could craft powerful equipment/buffs etc and also setup vendors in their cities. I was excited when I heard about strongholds but it turned out to be another instanced based update and therefore nothing like what I described.
Not sure they will ever do anything to give us incentive to revisit planets and that combined with a pointless crafting system keeps me a very casual player unfortunately.