1) The first thing I noticed is the 0/$9/$19 scheme. I would make it 0/$10/$25, it's more to the point and I think the rounded numbers would be better received.
2) I think you could make a lot more money. Large web development agencies could use this site to get quick feedback on new site designs. Not sure about your entire strategy but I'm thinking that you could "rank" reviewers. A reviewer who reaches a certain threshold is considered an "expert" or something. Then, offer those better reviewers to these development/design agencies for $99/month (or more).
3) Similar to point 2, maybe you could have a verification process for professional designers/website builders (prove they are good at what they do). They would (most likely) provide the most technical and potentially useful feedback. I think agencies would like to have these people give critical feedback which could be worth a lot... Like $300 / month. You could also provide incentive to professional reviewers with compensation ($1 / accepted review or something).
4) I would limit the # of reviews per site based on the plan.
Free = 5 reviews
Pro = 20 reviews
Gold = 100 reviews
Unlimited = Unlimited reviews
Not sure how many reviews are normally submitted per site, but you get the idea.
These are just some quick ideas. Like the site/idea, g'job.
source: Work for a web development agency.