Hi Scott,
Depends on what you use it for. If it clamps tightly and you're just filing in it, or holding two pieces together for drilling with a portable hand drill, it's probably OK. Also OK for light punching, chisel work, and hammering pins in and out, etc.
If you are bending sheetmetal in it using it as a brake, where aligment jaw to jaw is important, or you are depending on it not to shift for holding precision parts together, it might be better to get a new one from the major tool suppliers. Good vises are not cheap. Cheap vises are often not good.
You may be able to salvage the old one by dismantling it, building up metal by bronze welding on the worn areas, and grinding / filing back to a good fit. The parts need to be really clean and free of all oils and grease to do this, and ground to bare metal prior to welding. A lot of work, you may be better to just buy new, unless the old vise has sentimental value.
I've used many badly worn out vises in my time, you can get the job done with them usually, but they can be very frustrating and time consuming to use. A good quality well fitting vise though is a lasting pleasure to use.
Good luck JD