I agree. I haven't messed with Samplicio so I can't comment one way or the other about them, but over time I've received at least 15,000 credits from Ampario, My View and Peanut Labs.
It takes a ton of patience and a thick skin to deal with the frustrating aspects of the surveys. That's the price I pay since I can't afford to put much cash in the game and I want to play. I would suggest that if you can afford it, pay to play. Count it as part of your entertainment spending.
Please remember, though, that some of us need the surveys to even be here.