If you set your email, yes you will get spammed. Set another email (which you make as a junk-email). No you can not do a survey more than once, but they update with new surveys sometimes. I do not use this as I am not in US, and therefore gets error if I try. They will eigher mail you the code, or email you. But if you want it emailed, you will need to enter an legit phonenumber so they can call you to verify it. The paid/phone/creditcard ones give most points, but there is listed "Points: 1.25" or "Points: 0.25" or whatever it gives, below the banner. That way you can pick out the good ones.
Remember to allways click "completed"