Is the Wayne fortune old money? I don't know what the current continuity is supposed to be, but it seemed in the past like when Bruce's dad was a young doctor he wasn't rich. I assumed that he went into the military where he got training to be a doctor, then he ran a clinic, but maybe made some money from inventing a new medical procedure and then invested that money which left him well enough off, but still practicing medicine. Bruce inherits this small fortune and being a clever boy turns it into a large fortune.
Of course there were other stories that the Wayne family had a sterling past, but that didn't seem to have anything to do with Dr Thomas Wayne himself. But that was in the days of Bill Finger--I can't keep track of current continuity (mainly because it doesn't interest me).