Sorry for the late reply.
It is not a problem to discuss prices listed in references. As you noted, these are a useful indicator of
rarity and most collectors know they are not actual current values (but it might be helpful to mention that when posting them).
My issue with discussing prices is that the valuations given are often far from accurate, usually low. It often ends up with a race to the bottom with someone essentially bragging how little they paid - sometimes in
Bulgaria, or in 1997, or on an
eBay auction with a once in a lifetime
price, and they don't mention those things. I
price coins in our
shop for our consignors by comparing with what is on the market now and with recently closed
auctions; not with 1997, not with prices in
Bulgaria, and not with
eBay listings. It is not helpful for my sales when people believe that a coin I am
selling for $80 should be $40 because someone said so.