The biggest problem with group content in my opinion is a poor loot system. There is absolutely no reason to run T2C instances when T1 gives the same loot for much less effort. Turbine is taking FAs out of OD t1 tomorrow but that is still a band aid fix that will get people spamming some other instance like BG or spammy for their FAs.
In order to fix this issue across the board, I would recommend adding Supreme Essences to T2 and T2C chests to promote hem to be run. Also, each instance would drop different types of essences based off of difficulty. For example, a T2 Spambrog would drop 1 supreme essence whil sari Surma T2 drops 3. Giving equal reason to run both instances.