Many writers still have not discovered the power of POD. They attempt to use it in the old way, by hoping that somehow they will be able to attract the mass audience to their POD offering. This may or may not happen. Another thing that writers do is hope that if their POD hits a few thousand copies in sales, they will garner some attention from the mainstream. This, too, may or may not happen. Both approaches are a waste of time and effort.
What you should be doing is writing for the niche market. Forget about trying to impress the mass audience. You don't have the marketing muscle to do that. POD is not the back door to big publishing, either. Focus instead on the diehard readers in your genre of choice. What do they want? What kind of a book do they love reading?
Diehards are the keepers of the word-of-mouth. If you can impress the diehards, you will, very likely, also impress the heavy users, and before long, your book may become a cult classic. Cult classic. I think this is what POD books can legitimately aspire to.