On receiving more surveys...

One thing I've noticed: if I go back to an old e-mail invitation for a survey and attempt to take it again, after it rejects me, the link it offers to look for more surveys quite often offers me something that was never offered by e-mail or on the website.

And once I get one of those "surprise" surveys, I usually find that my e-mail offer rate goes up for a while.

YMMV