I'm certainly not saying you SHOULDN'T get a fitting, or that it won't help most people. But I finally came through with the money last year after 40 years of cycling, and they didn't change anything.
Well, they did--they said I should lower the bars, which I had level with the saddle. I raised them about 10 years ago, and it made me more comfortable without affecting speed. After the fitting I lowered them three inches for a week. I didn't go faster and my back hurt, so I moved them back up. Might be different if I were 40 years younger.