I had this same question recently when I replaced my broken stock charge pipe with the ER pipe. I have the COBB stage 2+ intercooler tune, so I'm running more than stock power levels. I asked COBB about the advisability of upgrading the stock diverter valves and here is the advice I got:
"Initially the stock valves should hold up very nicely. Heat and time does takes it's toll on them. If you want to be cautious, I would recommend the Forge BPVs. They have worked great on the our 335i stock all the way up to the aftermarket turbos. Hope that helps."
So, I plan to wait until my stock ones melt or wear out at some point in the future. So far, all the new plumbing is holding together.