I have been working on NetSuite for 4 years now. I have done SuiteScript 1.0, 2.0, workflows, searches, reports, etc (all normal admin and developer tasks with NetSuite basically). I am now certified Developer (meaning I passed the 2 exams you mentioned) and because I am a consultant I am now a certified ERP consultant as well. I will probably take the analytics, admin, and eventually SuiteCommerce as well.
So with that background, the answer to your question depends on what you want to do. If you are already working with a company who is using NetSuite, an end client probably doesn't care a ton about the certifications. If you are looking to get a job in this, then it may help you a lot. If you are looking to be a consultant, it will probably be a requirement at some point. For consulting companies, certifications help them look better to clients.
I also will add that I find that by studying for and taking the tests I have learned about features I did not have exposure to prior. This pushes me to learn those areas, talk to others, and better my overall skills beyond the exam itself. If you are only self taught, in my experience, you eventually fall into the "if your own tool is a hammer, than every problem looks like a nail". You won't have all the possible tools to do the best job