Outside of leves, what we've seen so far suggests that killing mobs in groups splits the base SP award from that mob amongst the number of people in your party and then applies the party bonus to that. So if a mob you killed solo would have earned you 100SP, killing it in a duo would split the base SP between the two of you (50 SP each) and then the party bonus would be applied (~40% for a duo) netting 70 SP each. That doesn't account for differences between ranks amongst the players. The relevance is that people claiming there is no group bonus for non-leve grinding are simply wrong. They're seeing numbers lower than what they might like and are jumping to conclusions.
I think that SE is trying to encourage people to group for leves. I remember shortly after launch Komoto made a statement that players were doing a lot of their battlecraft leves solo and that the devs would like to see them used for sort of a group thing. I think the difficulty is that it's just too **** much coordination involved to make it a truly group-worthy kind of activity. Not from the combat perspective, but just sorting out who is initiating the leves and this and that and...people just want to play. I don't think it should be necessary to have a "strategy" briefing for basic mid-rank content just to get people on the same page about starting the leves much less what they're going to do when they get to the fighting.
There's a lot of streamlining that needs to be done, and I think also that when the devs make a major change like the one to the SP system with the November patch that they need to be a little more descriptive in just how the new system works. Their communication has been far and away better than it ever was in FFXI, but there's still room for improvement there, too.