Well, that is the debate among lifelong stutterers. Most feel that the time involved in speech therapy and also the rate of relapse might not warrant the cost. Others are willing to try again, to try anything.
The Stuttering Jack blog has listed factors that can determine the length of time before a relapse could occur. I also see this list as one that could help you deal with the issues that could serve as stumbling blocks for success.
- The length of time that the fluency reshaping process was consistently applied in the clinical environment be it a day, a week, or three weeks.
- The degree of difference between the old innate speaking pattern and the new learned speaking pattern.
- The personality of the individual.
- The motivation of the individual.
- The degree to which consistent fluent speech plays an important part in the life of the individual.
- The severity of the disfluency problem.
- The environment that the individual will return to in employment, social, and family life.
- The support given to the individual in the change process, following treatment. 
So, is therapy important? It is if you deem it to be. Just make sure to take into account all the factors listed above. If you are dealing with negative feelings and attitudes about your disorder and you are letting those feelings determine the choices you make in life, therapy could be a good option to help you work through those, as well as, give you tools to better manage your disfluency.
As a person who stutters and went through therapy and still stuttered, it is my opinion that therapy does help. Again, my stutter is unique to me, and my results are unique to the therapies I've tried. It took me several years after my disastrous therapy sessions to reflect.
I reflected on my anger. I reflected on my continued disfluency. I reflected on my shame, anxiety, and self-esteem. And I realized I had to make a change. I was miserable because I was allowing my disfluency to control my life.
So I got down to the basics and analyzed my former therapy. I realized that between the four different therapists I had, three of them where pretty bad. The one in high school was overworked and had three students going to therapy together. That was a big joke. None of us wanted to talk, so she dismissed us with a scolding about how we are just hurting ourselves and how our lives will be harder because we didn't try. I had three therapists during college and two of them were equally ineffective. The common thread was that they didn't care about the fear I was exhibiting and would get angry with me when I couldn't produce fluent speech.
The one therapist that made the difference sat with me and asked me about my youth. She asked me how I felt when I stuttered and what I wanted out of therapy. She smiled when I said, "talk like you." Then she asked me to explain. "Explain?" I had no idea where she was going with this, but we got down to the core issue that I hated the sound of my voice and I was deathly afraid of the tape recorder.
So while in therapy, everything she asked me to do, she did first, then she did with me, then I tried it alone.
One day when we were listening to the tape and we were trying to figure out who was speaking, it clicked that I was fluent, yes it was at a very slow rate of speech, but more importantly I realized that I couldn't hate my voice anymore, because I sounded like her.
Unfortunately, I couldn't continue therapy so I left the same way I came in.
So here I was, years later at a crossroad in my life. And I made a choice. No matter how hard it was, or how weird I sounded. I was going to try again. And this time, for the sole reason that psychologically I was ready, Over time, I started speaking more fluently. Today, I have a lot of great days and I have a good number of bad ones. But, I'm in a much better place. I have spoken in front of a crowd of 300 people and I now teach graphic design at a university. And all this would not have been possible without therapy and without a therapist who knew that my psychological scars were deeper than the stuttering ones.
 "Speech Therapy for Stuttering - Is It For Everyone? (Part 1)." http://stutteringjack.com/speech-therapy-for-stuttering-treatment-adults-part1/