For me, the big issue is that these are V4 Characters, and I've gone almost completely over to Genesis 2.  As a result, your characters have just kind of faded out for me.  I'll probably get the Reese sisters at some point, but most of my budget is now going to Genesis 2 and other content.

The other issue I have is that Perez doesn't include multiple ages.  I've come to associate your name with multi-age character packs, which you do incredibly well (even before S4 came out ;)), but without that element, Perez is just another V4 Character, which I have way too many of as is.

The final issue I have is fitting clothing to your characters, especially the younger ones.  Most clothing don't include the S4 and Elite morphs, and the morph transfer processes in DS and Poser don't always do the best job of fitting clothing  properly.  Add to that the often mature nature of V4 clothing, and it's hard to find outfits appropriate for the younger characters as well.