So, 95% of my Nickel, Dime, Quarter and Cent collections after 1955 are from Mint Sets I bought and broke open. With that said I was always curious why certain years like 1968 had the SF Nickels omitted from the sets even though they were still outputting business strikes. Also, are the SMS from the mid 60's closer to business strikes or proofs? I have gotten differing opinions over the years, my opinion is they are high grade business strikes.
They didn't omit them. Look again, they are there in the Philadelphia sheet. (Philadelphia did not strike nickels in 1968, 69, or 70 and the San Francisco coins take their place in the Mint set those years). The only coins actually released for circulation that WERE omitted from the mint sets that I can think of off the top of my head were the 1971 & 72 P & D Ikes, and the 1979-S dollar.
Most people who like proof setsb think the SMS's are like mint sets and most people who like mint sets think they're more like proofs. This is why sales were so poor. On an absolute scale they're may be more like proofs but this might just show my bias. There are a very few which might be actrual proofs but the finest coins from these sets are almost indistinguishable from proofs. They are very well struck from basined dies and are even frosted in many cases. The worst ones are quite unattractive. There are a lot that just look like well made business strikes so part of what determines how they are liked might depend on different referents.
