I personally have been having a very hard time finding players to participate in the +4 group quests.
Wen I ask in general chat, usually the response i get is something like "dude, they're just dailies, skip them and move to the next planet"
I'm level 43 and have completed 2 +4 quests to date.
No point doing them, they take awhile todo and getting 4 people takes a while.
Personally I think forcing people to group is a stupid mechanic and just makes people skip the content (look at aion, you had to group to finish a area which meant if noone was around you had to grind....look where the game is now.)
I watched a guy last night asking in /1 for over an hour for people to join him in a 4+ quest....he eventually gave up.