It happened with stamps as well. Essentially, the price of a rare coin is what someone is willing to pay for it. In poor economic times, luxury / collectables drop in price as there are fewer interest purchasers. Whether the price recovers depends on how overvalued the items were relative to other investments.
There are people with a genuine love of coins who will continue to buy (on a reduced scale) during a recession, and there are those that invested to make money. The investees may not come back to coins, they may move on to china dolls or dinky toys. If so, any valuation bubble may have been popped.