all the math and numbers are on the upgrade table (Premium Account Page), but i think there is one more thing most people tend to ummm forgotten (or not realize), is the feel being a premium member.
it boost myself mentally, like confidence booster. because i know that my commission from referral and bonus are higher. from self-click alone (Ads) can cover the cost (maybe around 1% ROI each month). it saves time viewing 20 grids when i aim daily bonus. lowered minimum cashout limit make sure i'm eligible to cashout every month (i've been facing ups and down in tasking, so it's hard sometime).
but above all, i earned the money to pay my premium membership within 5 days - my first week in ClixSense by Tasking (CrowdFlower). so, nothing to lose.