Back in the old days it was mintages that were the primary determinent of supply for any given date but in the modern era this is no longer true. Mintages of all coins are so high everyone can set aside as many coins as he desires. Some coins with huge mintages can be tough or impossible and some with small mintages can be extremely common. But the '64 nickels were not only made in huge numbers but they were saved in huge numbers. There were so many saved that they are still beinmg released into circulation by collectors. It's not impossible that too many will get spent and the coin get a premium but it's very unlikely it will be in the near future.