I wouldn't go for a certificate. To me they are just a way for the guys that came up with the certification to make money, specially the Agile related ones.
I would rather focus on courses if you want to learn something new. To this day I haven't come across a job posting where a specific certification is a requirement to apply. (I've seen far more requiring a Master's degree).
If you want to advance your career in a more academic way, I would suggest to get a degree in CS, specially if you don't have one. Some people consider them a waste of time, but I think there are basic, abstract, and important concepts that you need to learn in order to be a really good developer. These topics will never be covered by just developing web apps.
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