Being an SEO pro I will say that I am a little biased. Without a doubt, there is a place for good SEO. With that said I approach all of my clients by looking into their business and seeing if good SEO is worth it for the business in question. SEO is not always necessary.
I have turned down plenty of prospective clients because the specific situation just simply would not require putting money and time into SEO. Sometimes the only thing needed is to simply optimize the existing website and content and send a few social signals and that can be enough to move the needle. Other times (in more competitive niches) it may mean you need a full staff of people keeping your eye on the competitive landscape that is SEO. The good thing is it is pretty easy to see when it is and when it isn't something you should focus on.
Here are three things to consider....
1. The Stage of your business... if you are a startup with a product you are still working on. It's probably too early for SEO.
2. Current Traffic performance... Have you found another traffic source? If so... How is it working?
3. Keyword volume... How much volume do your keywords get and are they intent based keywords or research keywords and do you want to sale through SEO or use it as an intro to the brand
Clearly, there are a lot more things to think about but this should give you an idea of how you can approach the question. The bottom line is with a little bit of research and discussion to determine what your business goals are you should be able to make an intelligent and educated decision as to where to put your time, energy and money.