Value and rarity of a 1964 US quarter with no mint designation and no copper sandwich center - what might it be?

Answer 1

There are very good reasons the coin has no copper center and no mint mark:

First, "sandwich" coins weren't minted until 1965. Before that, dimes, quarters, halves, and dollars were made of 90% silver.

Second, before 1968 the mint mark was on the back under the bow, not on the front, and Philadelphia did not start using a P mint mark on quarters till 1980.

Over 1.2 Billion 1964 quarters were churned out so they have no real interest to collectors. You have a normal circulation coin for that date, nothing special at all, but ...

The really good news is that the price of silver has gone up so much that your coin is worth about $3.00 (as of 09/2008) retail just for its silver content. Take it to one of those "we buy gold and silver" places; they may give you $2.00 or so as a wholesale price.