In mint state condition, the 1937-D is the second most common branch mint Washington quarter of the 1930s after the the 1939-D. In the early 1970s, this issue was priced very modestly, barely above the level of the Philadelphia issues. But several dealers recognized this issue as being more rare than the price and the Mid-1970s saw this issue being touted and promoted in price. Today, it has the recognition it deserves, i.e. it's not common in Gem condition, but it's certainly not a rarity.
Most mint state 1937-Ds are well struck and the typical example is white and frosty. This issue was available by the original roll throughout the 1970s. Superb Gems do exist and while not comon, can be found with just a little effort.