I haven't heard a pair of those since the late eighties, or early nineties, but I remember being impressed at the time. They were Allison's shot at state of the art at the time, and sold for over $5k! I listened to some before I bought my KEF 107/2s, and thought they were very good... just not quite the voicing I preferred, and the remote control & almost surreal imaging affects weren't really my cup of tea. They were pretty cool to play with though.
Allisons, of all vintages up to the mid nineties, are justifiably very well respected, but haven't developed such a following as to push their resale up too much.
For a collector, I think IC-20s should be something to shoot for as they were the pinnacle of Allison development along room interaction ideas, but they come up so seldom that it's hard to put a current value on them.
It would be a lot of fun to fix up a pair & play around with them in any case.
I envy you that!