Do you consider yourself to be a designer ?
Yes. I am a freelance Industrial Designer. mm2tts makes a valid point about the word 'designer' being very broad.
Would you seek the services of a professional designer ?
Yes, I often collaborate with other designers with different skill-sets and specialities. If I wasn't a designer, then yes I would. Though designers seem expensive, they are a crucial part of any products development and add value in all all areas. It's very obvious when an aspect of a product hasn't been designed by a designer, be that industrial, engineering, electronic, interface, or packaging designers.
Has 3D printing made you more aware of design principles ?
It is a great tool to make functional and/or aesthetic prototypes. Again, the term design principals is very open. In manufacturing/engineering design principals, it does on a basic level teach you about things like ribs and tolerances However, in other design principals such as Industrial design, it can only be used to PROVE design principals and your own understanding of them, such as ergonomics and aesthetics.
There are different 3D printing processes, each having their own pros and cons in terms of designing for their process. (SLA vs FDM). Even then, the part may respond differently when manufactured with a different process (like injection moulding, casting, or machining) and with different materials such as ceramics, metals, or composites. Though 3D printers primarily use ABS or PLA plastic, there are others that use metal, rubbers, and I've seen 1 or 2 that use concrete, ceramic, and even sand.
If your dissertation is really good, would be interesting to have a read. Maybe post it on the forum when your done?
Industrial Designer
Fresh Design Works (UK)
www.freshdesignworks.co.uk