Life_Saver

How about sprinkle in a few contacts that are "known" for giving out group missions. That way the people who don't want the group missions can just avoid the contact and others who like to group will know where to find these new type of missions.

A second thought that I had was keep the group missions where they are (within the story arcs) but give people the ability to choose an alternate mission in place of the group mission.

I have also seen 2 other types.
Some NPC's give statistics on your hero, such as "You have done 314 points of damage with your Fireball power today".
Also, there are some that praise your hero about specific missions (saved workers at X), general missions (streets safer from Hellions), and even task forces (Task Force XYZ sure has the goods).
Unfortunately, I did not take note of names, but I will in the future.