FWIW, I recently had a fitting, because I'm starting to race and have dramatically stepped up my mileage. At 50, my back and all my joints work fine, and I want to keep it that way. Could I have done it myself? Sort of. There's still no substitute for having an objective set of eyes check your form, take measurements while you're in position, and help you tailor your fit to a particular purpose. It also helps that you're working with someone who has shelves and drawers full of different length stems, a variety of saddles to try, spare parts to replace anything that needs it, and experience from fitting a few hundred riders and racers before you. A couple of bike mechanics standing by ready to swap things out is pretty nice, too.
The basic fit cost $75 and took about 2 hours.
The fitting also gave me enough information to go home and adjust my other bikes (my seat was too far back and my saddle was too low). Two races and a couple hundred miles since the fit, and I'm riding faster, longer, and more comfortably than I was before.
The same shop offers more advanced fittings, and also does machine fittings to help you pick a new bike. If I find myself still racing next Spring, I could see doing this again at the start of the season, maybe tailored a little more to the particular type of racing I intend to focus on.

BB