There are two types of diagnoses: the kind where your psychologist tells you you have it and puts it on your chart, and the kind where you take the national test (at least in the US), which has a year-long wait list.

I think what most people mean when they say it's not worth getting diagnosed as an adult is the second type, because the only thing it really does is force schools to provide adequate care for students.

I recommend seeking the first type though; I was diagnosed at 30 and it was worth it just to know. I only slightly suspected it though, and the diagnosis is what put me on the path to finding the communities, research, etc., which is ultimately what I got out of it -- so YMMV.

EDIT: Oh and meds! There aren't autism meds, but autism is often linked with anxiety or ADHD, and those can be helped with meds. Diagnosis is a first step to that.