I know I know, I have a vested interest in telling you the answer to this question is yes, so I'll temper that yes by downgrading it to a maybe.
You're a restaurant owner. You know that you have a market, everyone needs to eat and drink. Your dilemma is that people have a whole lot of options when it comes on how and where they're going to do their eating. To get them to come to you you need them to know about you. Now I know, you get plenty of luck of the draw customers who just happen to come to your place first or just can't window shop any longer, and maybe that's enough, and if it is enough than you probably aren't reading this cause you never Googled "Is hiring a food photographer worth it?" because you're content and rich and float through life on a silver cloud.
But that isn't you. You're here because you need more customers. You know about Instagram and Yelp, you've heard from customers and friends and bloggers that you should strengthen your online presence, but you've always been skeptical that it actually helps bring customers in. And I'll tell you what: Maybe.
Regular social media posts and a solid Yelp page are two things worth having just like a polished menu, a pretty storefront and and a friendly staff are worth having. None of them will win you customers on their own, but it's by checking off all of those boxes that you show customers you are legit and worth their money over any other restaurant, because if you don't have them, the next guy will, and you've just lost simply by not having something.
ACTUAL TALK ABOUT PHOTOGRAPHY'S ROLE IN ALL THIS
Sorry, I hate fluff too. So You've got your Yelp page, your Instagram and Facebook, your menu both in brochures and up on the wall. All of these things are more impressive with even just a few very well done photos. You don't even need a lot; a few amazing images are worth more than 30 blah ones. No one's looking at all 30 anyway, so make those 5 images people look at really blow people away OR hire someone who does that professionally! Because you, dear restaurant owner, are not a photographer (unless, of course, you are). Your photos are beautiful, and I'd never tell you otherwise to your face. You took them with an iPhone, you're been told their built in camera is a bajillion megapixels, but I'm sorry to tell you that portrait mode is parlor trick software and that if it really were that good then the entire commercial photography industry would have been put out of business by now. But it hasn't! In fact it's bigger than ever. Which tells you that a professional can create something special, something that might really be stunning enough to lodge in someone's memory and change their consumer behavior three month from now. So consider what just a few beautiful images could do.
Let me pose it to you like this. Every time you have an interaction with a customer, be it online or in person, it's like you're at a job interview. If you show up to a job interview wearing a stained shirt, act rude, and give vague answers to all the questions, you aren't going to get the job. As a restaurant you have a dress code, you employ friendly waitstaff and you produce quality food to impress customers and ensure they come again. Now in this metaphor your restaurant's website, Yelp and Instagram are your resume, LinkedIn and Facebook. If you don't have all of those things looking polished and well-maintained, you don't ever even get to the interview. They have 20 other candidates who do have those things and even if they see you have some good experience you're clearly not that invested, so they move right along. Placing a few great photographs online across all your channels shows customers you're serious and will place you in contention. Because remember they know nothing about your food or your restaurant! You know your food is delicious but you need to convey that to someone who doesn't know if you're a palace or a complete dump. You have to SHOW them.
You'll have another feather in the cap of a truly successful restaurant. In other words, you have to dress for the job you want, not the one you have. In other words, people will pay more for food if they think you're the kind of place that hires a professional photographer.