I think I have had about 7 Honda CB 550 K's, all years from 1974 to 1976. They have all been hard on the clutch, more than what I appreciate. Always replaced the clutch wire, but it did not make any magic difference. I now plan to replace the springs, but from what I can read on this thread I probably should not expect more magic. But do check the routing of the wire so it has a "free float" from handle and down, I have seen bikes where the routing has been poor.
However, yesterday a friend of mine visited me on a 1975 CB 550 K1, very nice bike with 6500 miles. I checked his clutch, and it was very smooth! No real force needed!!! Made me wonder....