If it is just ground water and not coming in then go ahead and fill it in unless you do need the perimeter drain system but it may not be a big enough area (24")to make a difference for a drain. If you have gone 45 years without any moisture problems or need for a sump pump, then you should be ok.
Remember also that termites can come up through there so get it sealed. Make sure it is rot and not termites. Also as suggested, use treated wood on top of concrete. Good luck.