[phantom_oracle]

There's not enough space here to give you a complete outline of how to do things (and whether or not it will work).

All I recommend is this:

Find similar plugins (not necessarily in terms of likeness) that sell about the same or make a little more money and deal with the same level of clients (eg. 500 people buying).

Sometimes the best thing in such situations is to do nothing and just leave the passive income stream as it is (although if you identify a positive demand for a product that requires better paid support, etc. then you can probably grow revenues).