It’s really entirely up to you. If you feel that making more observations has value, then please do so. iNaturalist data are used in many ways, and there is no single scientific end for these observations. Recent publications based on iNaturalist data, for example, have included an analysis of shelter types used by frogs, variation in colour and pattern of grass snakes, and analysis of plant species visited by one species of butterfly. I imagine that few of the observers expected their observations to be useful in these ways.
For most species, I personally wouldn’t add more records for species I’ve already recorded in a county and month, unless there is some other motive for doing so (an interaction with another species, an especially informative photo, a bioblitz…), and certainly don’t let it become a burden, but if you enjoy making such observations, please continue!