The OP replied to me that the currency was still redeemable (to APMEX for silver). My point is that if the silver certificate could still be redeemed for a dollar's worth of silver (ten dimes, four quarters) it would be worth $20 in 1964 dimes. Yet the change in the composition of the dime in 1965 and you get $1.
When I was a kid in the 70s my grandparents would save the large seal 1934 Federal Reserve Notes and give them to me for my birthday and in holiday cards. By the late 70s I had about $150 face value in $5s, $10s and a couple 20s. Most were in lower grades. At the time, you could get a decent 1909-SVDB for $100-150. I really wanted an SVDB but didn't have the money. Move forward to the late 90s. I finally bought an SVDB for $450. I paid for it using $150 in worn 1934 FRNs and $300 in regular cash. Even though the old notes had "value", the most I could get was face. The moral of the story is that I would have been better off using the notes to buy an SVDB in the 70s. Holding onto to their value cost me $300 that I could have used towards another coin. All that said, your worn silver certs are worth $18 in the real world. You may find get lucky and find somebody to give you a 10-20% premium, but how much time and effort is it worth to make $2-3?. In 20+ years, you'll still have the same problem selling them for more than face. IMO, use the $18 towards a coin you want.
I was mentioning that inflation has increased the price of silver since the 1960s. In 1932 for example gold was redeemable at $20.67/oz. Now in 2021 gold is redeemable at $1920/oz. But it is indeed redeemable. Just not through the government.
There is a dealer in Cranston, R.I. who sells circulated $1.00 silver certificates for $125.00 per hundred, so pretty sure he is just taking them off someone's hands for face.