Hi Thomas
Part of this may come back to your country and the the value of such a qualification. As you mention Germany it seems quite different to my country: Australia. Of course, a PhD is quite respected but culturally most people don't introduce themselves or use the title of DR unless the are a medical practitioner (which is amusing as they don't actually obtain the academic level of PhD).
For me, going for a PhD would be a personal goal and unlikely to improve my job prospects. In some situations, it might have employers in private sector concerned that I'm too caught up in the theory and academia life as opposed to the real world. I did consider doing a PhD when I was at university but I must also admit, it was so I could call myself Dr Mikki (has such a cool ring to it as an 18 year old).
Where a PhD might come in handy is if you are trying to get into the research arm of SAP. By choosing a developing topic you could become a thought leader in it or network with the people who are creating the new technologies.
The other consideration is if you want to end the world of academia and stay there. Having a PhD would create that career path.
But within the SAP world, I see it as more personal accomplishment. For me, I'm furthering my qualifications through private certifications - SAP and other industry/non-vendor specific. To me, I need the qualifications that are recognised within my industry and amongst my peers who will consider me for my next role.
Regards
Colleen