Yes, air filter elements should be replaced about once a year or more often with a lot of rural miles. If your engine runs better without the filter its well past time for a new one.
This is the same 37mm high element that fits single HS2 carb or HS2 twin carbs.
The Cooper filter cannister that requires 2 filters was not quite so deep and therefore required the filter to be 37mm high as opposed to the original single which was 40mm high. For K&N elements see E-9001.