The ABS question is a very general one (no matter which bike you're interested in). Is it worth it, paying for ABS?
Well.. there may be situations where ABS might save you. If you are a good rider (by which I mean not just ability to use controls properly, but being very aware of your surroundings), you should never need ABS.. and you should definitely not depend on it as a necessity.
This is a highly arguable point and you will get plenty of pro vs con opinions, so ultimately it's up to you to make the decision.
As for used FZ1-specific issues: carefully check the frame welds. There have been several reports of cracked frames, especially on older models (06-07).
Besides that, I would do the normal used bike check (universal issues associated with used bikes). You can find excellent examples of such lists by doing a google search.
Good luck!