I vote that you keep it.

What do you mean by "modern"? Do you mean modern as in a current steel production bike or modern as in componentry? Nothing wrong with current made bikes, but unless you're going with something like an indy fab, gunnar, etc... I doubt they will ride as well as your centurion (if it fits you of course). As stated earlier, if you really like the bike, keep the parts and modernize the the componentry. I love the feel of retrofitted bikes.

I myself don't care for keeping bikes original when I am riding them. I build it to how I want it (*and what I can afford*). However, I think keeping the stock parts is important when you are reselling. So box up all the parts, let them collect dust, add what you want and enjoy your ride.