As far as I know, they were overpowered because the high price sellpoints were too close to the mining fields (Cali Minor). I think copper should be restored, as the Denver sellpoint is not that close (5 systems away), and/or tune the Denver sellpoint down a LITTLE (9900-->8500-9000), and give an other max pice (10 000) sellpoint for O7 copper (somewhere 6-7 systems away from O7; tuning up the Narita outpost price to~10k would be ok).
In that case, I don't see why the fields have to be turned off then. it's the Devs/Admins fault for turning up the price of silver (which they said would last a few days) but then forgetting to turn it off.
This problem isn't solved by nuking the system completely, rather by just lowering the sell point.
Copper was fine though, it didn't have an OP sell point or anything.
The default, non-boosted sellprice was also too high on Cali Minor, due to the short distance: ~9500/piece; distance: 3 jumps.
Now all high price (~9-10k) sellpoints are at least 5-6 jumps away from the high yeild source of the mineable commodity.