About the only thing I can say is Shimano hasen't changed the mounts of the components so if the 600 series is junk (I don't think so) then you can upgrade fairly easily with new gear, I also have a vintage bike or two and the old Shimano stuff still works great with a little TLC and lube, I have a 1980's Cannondale with all the original stuff and it still rides great.
Good luck.
Spike.