The spread seems to get even bigger: user 51 has 1223 click, which earned him 0.00004360btc, while user 43 received 0.00092286btc for only 3 clicks. That's an about 21 times bigger payment for only approximately 0.25% of the clicks.
While I'm in no position to tell you how to run your project, I can say that webmasters want to be able to do some rough guessing. I know it's unfair to compare it to Adsense, but there I can do some estimations. Here I see differences of up to a factor of 8545, which, if applied to Adsense, would mean earning either $0.01 or $85.45 per click.
From my position as a webmaster it would help to have at least a guaranteed minimum earning, even if it's just 0.001btc per click.
Thanks for your feedback.
User 51 has 1560 unique impressions and 1223 unique clicks. I don't want to say anything about user 51 since I don't know who he/she is and how did he achieve this ratio. But it looks suspicious and he/she could receive ban instead of money from Adsense.
Guaranteed payments for clicks or impressions give strong incentive for fraudent clicks and impressions. If I knew the minimal cost of fraudent click or impression, maybe I could set up a guaranteed payments below that cost.