I am not a fan of paid posters for many reasons.
One reason is because of what it is saying - ie. That the regular posters are too stupid or do not care enough to post a lot or the site is so uninteresting that nobody posts.
From a strategic perspective, it is a lose-lose situation. Paying posters means that the "company line" will always be the loudest. That will have a negative impact on all who would be considered "respected" posters as well as the inclination of people to post dissenting opinions.
When people are disinclined to post a dissenting opinion they usually move on to a place where they feel comfortable.
Look what happened to BW, MW and possibly starting to happen to the RX.
Do you really want to lose the voices of dissenters and respected posters for a jump in hits today?
This is a different world than what existed a few years ago. There are no short-cuts. There is a great deal of competition. Hand in hand with the rise in competition is the overall lowering of quality.
Check your business history. What happens when industries grow fast? When shakeouts occur, who survives and why?
Then again, the most important factor is what you view as your role with this site - ie. Is this something you plan on doing for a while or are you in it to make a quick killing and move on.
If the former then some deep thought is required, if the later - why waste your time asking the question?
Good Luck,
Joe