I want to add a vertex to an edge of a poly and I want it to get a mix of it's neighbours attrib values. This is really awkward in vex and I was hoping that when I now face this problem in hdk there would be some advantages. Or do I need to find all atttibutes, loop over them and mix their values per type?

I think it's going to be easiest to create an GEO_HedgeInterface [www.sidefx.com] and use its divideHedge() [www.sidefx.com] method (or use split() if you want to add extra polygons to accomplish this).