We haven't tried the Poly yet (doing that for the first time in Sept), but I think for the $30 difference, I would go with the Contemporary TPV. I have two favorite views at WDW -- Boardwalk view at the Boardwalk, and Theme Park view at CR. The Boardwalk view is something we go back to annually, while the TPV at CR is something I'm really happy we did once. I don't feel the burning need to do it again (I think mostly because of the price), but for that once, it was super-magical. I don't buy the "it's a parking lot view" stuff. Yes, you do see it, but think of it as wearing bifocal glasses. Down is parking lot, straight ahead and up is pure magic. Just don't look down.
Of course it is a recurring question here regarding whether the TPV is "worth it," and I would say you have to balance my comments above with the price. If you can afford it, like I said, it's definitely worth doing once. But if it really makes a big difference in your budget, and/or would impact your spending on other things during the vacation (dinners, souvenirs, etc.), or impact future vacations, then I agree with the sentiment that being at the CR or BLT with a Bay Lake view is better than breaking the bank for the TPV. Hope this makes sense!
(ps -- Just to clarify the "if you can afford it" comment, often affording it is a factor of things such as discounts offered, seasonal pricing, length of stay, etc., more than any net worth!)