There are limitations to using the Gordon model. The most obvious is that not all stocks pay dividends, and so you must use a substitute measure, such as earnings or cash flow, to apply similar valuation techniques. Also, assumptions about a constant growth rate indefinitely into the future aren't very realistic, and changes in the cost of equity capital can also result in changing stock prices even under the model's own terms.
Nevertheless, you can get at least an idea of implied growth rates stemming from changes in the stock price. The key takeaway for investors is that if you disagree with the growth assumptions that a given stock price implies, then you can make stock trades to take advantage of that disparity if you're right.