First, and most importantly: a ground plane in the model preview.
I've lost count of how many hours I've spent making little adjustments to make an object not "stick in the ground".

Since Sims 2 meshing is largely guesswork the more of this that can be eliminated, the better!

Ok, here's a really big addition: Modify the Wizards of SimPE Recolor Wizard to allow the loading of custom objects.

Improved documentation: There are so many features, and so much guessing. Having some improved documentation would *really* help. I know, there's only so much we know about how all this "stuff" works, but the more those of us using this know about what stuff is and does, the better we can make things.

Finally, fix the handful of bugs. I haven't run into any serious ones, but the couple I have are annoying.

Pax,
Indigo