>>> What would be really great is a place where all non-V4 accessories [clothing/hair/props] have been converted from any other proprietary model for easy and convenient use with V4. 

V4 already has pretty much any type of clothing imaginable. But since a good part of it has been made in the Poser 7 and earlier days, it might be better to update what is already there than to convert clothing made for other figures.

By updating I mean updating from legacy falloff zones to weight mapped rigging, and updating FireFly materials to SuperFly. However, the original content creator has to get involved with that because the updates would be derivatives of the original geometry and textures.