Two ideas i had, that roughly stem from other mmo ideas.

1. Create dungeon puzzles that take character's weight into account (much like the Tonberry dungeon in FFXI). 4 lalafel could be the equivalent of 1 Roegadyn in terms of weight, to trip certain switches. As a balance, only Lallafel are small enough to reach switches to aid in access to alternate dungeon paths.

2. Allow certain species to have a species specific ability. It could be subtle or short term for balance, but still something that allows distinction. Something that would have a player be given a sense of personal pride to have, and a similar jealousy of the other ones they cannot have. For added variety, you could even split them into tribes, like Dunesfolk versus Plains Lallafel.