I'm not familiar with the NwN scripting language, but after perusing the forums for nearly 12 hours so far today, I stumbled across a long thread regarding excessively large groups (resulting from continent-wide tells to friends).
A few things that I noticed in common with a majority of the posts were:
1) People grouping would be from a wide array of level ranges.
2) People grouping would often be from other continents at the time of party formation.
To circumvent this, is it possible to use the scripting in NwN to limit parties to x number of PC's with a level range that is +/- X of the party leader?
For example, if the party leader is level 10, other PC's of level 8 - 12 could join. If someone that is outside of that level range attempts to join, they could be issued a "You can't join that party" message.
Again, not knowing what the limitations are with the scripting language, I'm not sure exactly how much limitation there is over the control of in-game mechanics. If there isn't a whole lot of limitation, you could even go so far as to limit which alignments could form a party together.
Just a thought or two, with the intent of trying to solve a gripe that I've seen on the boards.
~Raythen, anxiously awaiting character approval~