At what point would you step up to ferrea hollow stem valves

The only reason I have made it through 47 years of racing is I believe in the keeping it simple (KIS) method of engine building. I save money where I can and spend where I have to. I’ve gone 8.40@160 mph with standard stainless steel valves in my big block and 9.42@138 in my small block without “fancy” parts. The last valve spring I broke was back in the 1980’s I broke three inner springs with a 750 lift cam engine that I raced three days a week. We found the issue and it never happened again.