I probably wouldn't do it unless you're after just one or two spares. One thing to check is the amount of carbon deposits on the tips of the coils, check that the boot is not dried out or cracking, and check that the coil body does not have hairline fractures (could indicate that spark is being lost through one of these fractures).
Having said that, if you were to get a set dirt cheap then they may prove handy one day.. you're bound to get one or two good ones in the lot. I collected about 6-8 spare coils on my last car.. CA18DE.
If you're planning on replacing all 6 coils with splitfires and you're worried that when you hit boost you'll start misfiring, i'd probably ask for some sort of guarantee before you bought them.