My guild is inviting eachother to arenas and danger rooms left and right. Thanks to elevator and arcade costs being removed, that's a thing you can do now.

There's no monetary gain in inviting friends and guildmates to cool stuff, only the sense of camaradiere. There's nothing to lose on inviting friends places (provided they're not so bad they drag you down, but that's always been the case), so maybe stop being so cynical and think only in terms of loot and efficiency.

Also, everyone gets every mineral from every party member, so that's a pretty big dang incentive to party up.