Kcat,
Not had much chance to further test my 012's. I do really like them for stereo applications, not as much of a fan using it singular. I prefer the 102, 4047 or Kiwi for that. Personally, can't say i'd use anything other than cardioid for my purposes. I tend to record things fairly directional because my room isn't treated as much as i'd want, and bedrooms don't really have much of a cool vibe (sound wise) which is when you'd be reaching for an omni.
I do like the 012's for stereo acoustic guitar. I really like stereo for when the guitar part is isolated in the track as it gives a much more dynamic feel to the left/right image which makes the soundscape more realistic and have more depth than a mono track, even with reverb. You can't go overboard with stereo though because it starts to make things difficult with panning and phase correlation, but on certain things, it can sound sweet.
For the price you've been offered, i'm not sure if i would take it, simply because it's almost the same price as a new set with the same capsules, at least here in Europe. If the extra capsules aren't a priority, i'd see if you could order a cardioid stereo set for less. I am impressed with the sound as mentioned, but like me, you also have a half decent LDC, so i wouldn't worry too much about extra polar patterns unless you think you are going to need them.
Did you go for the A7X's in the end or are these to demo? Either way, see if you can grab a high quality version of John Mayer's latest album (Born and Raised). I really like the old school feel and dynamic of the production, it's so original but also fresh to listen to. Any Norah Jones is also a great (Creepin' In is a cool track). I'd also bang out a bit of Steeldrivers whilst you're at it. I'd also recommend listening to The Wailin' Jennys (40 days). Again, production is spot on to me. Being canadian, you're prob already one step ahead of me on that one perhaps?