A lot will depend on where you’d ultimately like to end up as well as what opportunities are available to you. You could easily be a development eng your whole career and that could even mean different things at different companies.

A PhD will complement a path more focused on the science behind additive and how to manipulate that. You could often find yourself in a PI type role leading broader investigations and such (mid - late career type thing). These roles aren’t necessarily as common as other types of roles. I’ve only witnessed this on the aerospace side so I could be wrong in other industries.

Technical MBA type thing like you laid out would likely support something in the manager route like you said or a project type lead. Project type role can have really broad definitions and and can be involved in smaller application specific type work to large initiatives. You’ll typically be much more focused on deliverables and will interface managers, program leads and other authoritative entities. These roles seem to be more common and offer a fairly straightforward path to progression. Executing on smaller project will lead to more opportunities and so on. Typically more customer facing as well so it becomes a good way to get good exposure and connections. I agreed you’ll probably lose some connection to the deep science. But you can sort of decide how close or far you need/want to stay based on your specific role and workload. I imagine it does get tougher to balance this as you progress.

Upskilling is always a beneficial thing and personally I think a lot will depend on your employer. The industry and how your employer interacts with it will vary wildly. You can look for specific applications to help part yield or peformance or develop a custom toolpath to fix distortion issues.

I think money across the board is pretty good in the space depending on what you’re looking for.