The promo cards actually aren't that valuable, except Fatty Bolger seems to be a bit more rare and he is a great card.
Certain cards might be worth selling separately:
- METW: Assassin, The One Ring.
- METD: Nothing really, these boxes are cheap.
- MEDM: Not much either either... maybe a few rares but I don't think it's worth breaking up the lot.
- MELE: The Lidless Eye, We Have Come to Kill, The One Ring, Chill them with Fear, Elf-lord Revealed in Wrath, Uruk-lieutenant.
- MEAS: The nine R1s: The Ithil-stone, Farmer Maggot, Angmarim, Nûrniags, Bairanax Roused, Daelomin Roused, Eärcaraxë Roused, Itangast Roused, Leucaruth Roused.
- MEBA: Best to sell as a complete set (not just 1 of each) as it is the "rares" that are valuable, not the extras cards. Stripping the rares to sell separately for sale separately probably it too much work for maybe no better return. Longbottom Leaf is especially valuable, Sauron as well.
If you just post up a list of what you have you may get a better response to determine what partitioning makes sense.