The only thing I would add is that the exception to the rule seems to be the 50 mm 1.4. The older SSC version is by all accounts superior in durability and optical performance, as well as being sharper wide open and even brighter to look through due to the larger front element. Other than that, buy the newest lens in the best shape you can get - within your budget.
EDIT - Sorry, just realized I was not making myself very clear there: my comment refers to new FD vs old FD, not FD vs FL . I always looked at it this way - FD lenses are what I use, but its nice to know the FL's will fit if need be. It seems that the coating technology has come a long way between the FL and FD range - the FL's seem to be quite sharp, etc., but much more prone to flare, some claim contrast issues and colour balance. The flair is the only thing I can attest to myself. And the price difference is not that big, really.