Just test it, create three different apps and see which one makes the most money (you could skin them differently or perhaps you might just need to have a different icon).. of course there are other issues such as a reduction in virality (if you depend on it) however you will be in a much better position to estimate once you actually know how much people are willing to pay.
Is there any use of iTunes affiliates in the app? Like you have a 'beautiful wedding songs' chart & then you profit from any songs they download because of your app?
It would also be good to have paid for content - like pre-chosen track listings, affiliate sales would be high for this too!
