I've found mirago very odd- they deliver very little traffic at all but the £25 I sent them almost two years ago has not run out. So they are still sending the occasional click through. I think there have been a couple of sales though so I wouldn't say it was a total loss. Just don't expect much from them.
You know the £25 is to keep getting your site spidered don't you. Mirago send their bot out every 7 days, 48 hrs and 24hrs. Maybe you have a tons of entries because of that, and that's where the clicks come from.
I've heard stories about Mirago being big - very big and sending a lot of traffic. In the early days the high street banks laughed at them, and now they kiss Mirago's kneecaps.