A good question.
For some time, I've been considering buying quality covers for my stories.
On the plus side, a good quality cover can encourage sales of the book.
On the minus side, the cost of the cover needs to be covered before I'd see some small profit, and although $69 is a small price to pay for the beautiful covers on http://www.selfpubbookcovers.com/. I would need to sell about 15 copies of the e-book to get a profit.
A lot of people, for a long time, have told me that I am a great storyteller and finally I'm beginning to believe in myself.