The "Purest" vintage collector/operator would still use a battery. There are many folks that are worried enough about the "collectors value" to not want any custom changes.
I know a local that buys/sells/trades too often to bother with any updates. He keeps about 10-20 trains at a time max. He only keeps three long term.(a Hudson, Vir. FM-TM, and a prewar tin steamer(#?)