I used a KMC link with a shimano chain until the chain wore out, since then I have been using KMC chains with KMC links. I also wax my chains (with graphite mixed in) but I get between 500-1000 miles per treatment, so I have used each link probably 4 or 5 times. However, once I dropped half the link outside when cleaning my bike, so I reused half of an old one I had hanging around. That half went significantly more changes.
I'm not sure the link wears like the chain. My understanding (which may be flawed) is that the wear and elongation occurs in the holes that the pins go through, not in the pins themselves. The holes on the link are not load-bearing, they just keep the link linked. I know my old links look the same as the new ones, just less shiny.
Having said that, the KMC chains (and Nashbar and Performance, which are also KMC) come with a new link, so I do change them when I change the chain.