How old is your child? I think age makes a difference in many different ways. A lot of times the sensory stuff is obvious early on but in later years other issues develop or become more apparent--or don't at all. Not trying to say that your child will definitely have other issues. But if he is 3 1/2, say, I think it is a totally different situation from eight.
That said, yes, our play therapist has been invaluable to us. She has really helped us understand our child and learn to parent him better. She has also helped him develop an emotional language and learn some calming strategies. She has also observed him at school, talked to teachers, etc--she is our go-to person and a person I trust and rely on. OT, on the other hand, didn't do a lot for us.
I think the important thing is to find SOMEONE you trust and who understands your kid, whether it is a developmental ped, a psychologist, psychiatrist or other therapist.