I decided to split the gang up for a few reasons, but the main one was that keeping them together would produce a group of such size that the individual characters would inevitably get very few lines (as in real life, the few dominant personalities would end up speaking for the others).
I guess I can summerize them as follows:
1) Offers more Plot oppertunities as well as exploring more of the world that otherwise would never be seen (like the Feral Forest, the Abyss Lake, etc). It also allows for the two groups to have wildly different interactions both with the main and secondary villians as well as the good guys.
2) Ensures all characters get the 'screen' time they should get, while allowing space for new and interesting characters to be added and developed.
3) Allows for a 'break' from a certain storyline in favour of another.
4) Allows for multiple villians and cases of villiany. For instance, did you notice that there was a big switch in the story where the villian that terrorizes one group gets taken down by the other?
5) Gives you a different impression of the same character from two different groups in some cases (ie with Glide and Star).