Well, you're not actually reviewing the product. Sure, I wouldn't mind a time series of the price history of an item esp in cases with large jumps. But, generally the point of reviews is to tell me about the product. I can do my own evaluation of what I am willing to pay.
Hijacked product pages and price swings are two of Amazon Shopping's biggest vulnerabilities from my view. Do you know of a price history website/app like you're describing? Sounds like a very good idea.
