Bob,
My first question would be what are you trying to get +1's for? Is it for your domain, specific link or something else? We wanted to have more +1's for our site, so we added a +1 button on our homepage so people could +1 it on the fly. It worked out and we now have 41 +1's more than before.
Also, what we have found is that an incentive doesn't always work. It's a bell-shape-curve and after a while it will actually have a negative affect. I agree with Peter, sometimes all you need is great content but what I do strongly believe in is reminding people to do it. You could be on Yelp but if you don't tell people you are there and the fact that you appreciate their feedback, you won't get as many reviews. Same thing with +1's. Let people know you would appreciate the love, if they enjoy reading your content and they can decide if they want to +1 your link or not. If it is good content, it will work every time.
Add that button to the target, it works like a charm. If people see it, they will remember to do it.
I hope this helps.
Best,
Ashkan Sobhe