Many micrstock photographers reported reaching a plateau in sales at certain point. I experienced it myself several times. I mean I continued to upload new photos but my sales per month remain flat.
On the other hand, if I stop uploading for a long time my sales remain flat too, though at a lower level. Some other photographers mentioned the same phenomenon: they stopped uploading for some reason, sales drop at first (up to 30% or less), but then they remain stable for a long time.
For example, Jonathan Ross has mentioned that he continues to get a stable income after he didn’t upload to microstock for 2 years.
The conclusion from these 2 observations is simple:
Every portfolio has a threshold. If you supply the number of photos above the threshold your sales will grow. If you supply below the threshold the sales will stay flat.
The threshold goes up with the growth of sales.
My current threshold is around 60 photos/month. If I upload 50 in a month, the sales remain flat; if I upload 75 or more I am starting to see the growth. Thus I am trying to produce 80-100 photos a month. And I know I will need to produce more than that when I’ll reach a new level in a few months, to keep the sales growing.