I think there is a quasi collector Numismatic market that folds into pure bullion when the metals run. There include modern 'rarities' such as Eagles, etc... On the other hand, as you point out, the vintage rare coin market is pretty well divorced from bullion. People won't sell a BU 1893-S Morgan dollar for melt even if silver goes to $1000/oz.
Yes, but a rising tide lifts all boats. The modern market in silver, gold, and platinum often consists of 'key' dates within particular series that fetch premiums over other more common members of a series. As the price of PMs rises these premiums become trivial, as melt price rises above what used to be the price of a premium coin.
I used to collect proof platinum eagles and there were some 'key' dates that were more expensive because the mintage was low. When the price of platinum ran up toward $2200 I sold them all, mostly based on melt values. I can already see this phenomenon taking place with the way dealers are selling precious metal coins this week. They are lumping together more coins and eliminating premiums based on what they can get for the coin at 'melt'. Many years of slogging through sideways price action has them eager to offload at a higher price based less on rarity and more on spot price.