Well talked to the owner of the shop today, he informed me that no they will not just buy any pre-1960 nickel. To get $0.15 it has to be pre 1950 and it has to be in Very Fair condition or better. For him to purchase a pre 1960, it has to be in pretty much Uncirculated Condition. I was a little disappointed, but it makes more sense. The only one he bought was the 1938 nickel I brought in.
Very Fair? Did you mean very fine?
Either way, your first post seemed too good to be true.
1940-58 wheat pennies are worth 3 times face value but Jefferson nickels of that era aren't.
Ultimately there is less demand for Jefferson nickels.
The only way I see that changing, is if the composition of nickels change, and the government start culling the CuNi.
I had some luck sells rolls of 1940s and 1950s nickels on Ebay, but it wasn't consistent.
Currently as far as Jefferson's go I keep the following:
War Nickels
Key/semi key dates (1950D, 1938 DS, 1939DS)
Error coins
1942D, 1948S, 1949S, 1950, 1951S, 1955 (not considered semi key, but low mintage, < 14 million)
1938 and 1939 (not worth much but they're 75-6 years old)
all 1940-9 that are at least VF
all 1950-9 that are at least AU
Proof coins (not worth much, because they are all banged up, but I don't find many)
Canadian: all 1981 and older (older ones have numismatic value, newer ones are nickel bullion)