Grouping:
A MMO should encourage People to Group for a quest.
Grouping itself has become lesser important since the uniqueness of the different classes got blurred caused by serveral known reasons. DDO is a game and it is Business. To Keep as many Players in line to Play the game as possible, compromises were done and taken to not lose the not-dedicated players, who would Play anyway. Selfhealing for not-selfhealing-classes by EDs broke it the most. The cries for not-filling raids etc were too loud at some day coz not everyone could Play every quest ... awww.
This, and maybe pl+powercreep and op, have contributed to the trend that People are or became soloists. "BYOH" and "cope alone or stay out, i can´t or won´t take an eye on you" are some Kind of Standard. And the most can cope alone today if not "gimped". Close to everyone can do everything, selfheal, trap and deal high DPS atst. As Long as These "mechanics" are not removed, there will be no Change in grouping. Besides the fact you like grouping anyway and run in a Group or not.

So, why grouping anymore? Just for the social aspect? Grouping even on the highest difficulties is just needed for raids, hell even those can be soloed.
Honestly speaking with everyone so powerful, there´s no Need to reward grouping with more xp for the quests. If one can solo anyway, a second, third etc Player makes it easier anyway! Dungeonscaling doesn´t Change this. The more, the easier.
So there is already a reward in xp coz the quest is faster finished and the xp/min IS already the reward.

If there was a quest in concept designed for 3-4 Players, this should Count for the "100%". Be glad you finished and got the xp.
More Players make it easier and one could say it should give lesser xp. Rewarding with more xp is simply paradoxical.
Lesser Players would make it harder and one could say it should give more xp. Rewarding with more xp is simply more Logical. (Hello soloists!)
But both ideas are bunkum. There´s a quest, it rewards 10.000 xp. More or less Players doens´t matter.

Flawless Bonus:
For what reason this anyway? To be proud we´re so uber? Ok, i can understand the Feeling of being happy "we did it" and nobody died, but this Feeling is defined by the difficulty i ran it. Elite. Wow. Did it, yeah! Elite rewards more xp than hard.
If "Flawless" still shall stay in the game, start every quest with a -10% Penalty until quest is over and then void it. You want to stay your buddies alive? Then take care for them and Keep them alive. That´s a reward. People die in the beginning as noob and People die later when pro. This would be the only "team-Bonus" i see at all.

Bravery Bonus:
Another "I´m-so-good-so-i-deserve-it" Bonus that´s not neccessary. Reward 1st time Bonus and take difficulty into consideration. Once a quest was done on high(est) difficulty, No quest even on a lower difficulty should break your streak, just have it paused or uncounted.

Most of These boni in my eyes seem to be just for the reason to be rewarded higher for lesser playing and faster leveling. And the fact that "But we have no time".