I stumbled upon this old thread of mine and tought it would be appropriate to report on the outcome.
Since the offer above, I really was offered a Team manager position later. I declined.
It was not much more pay but much more stress.
However I did got a (somewhat unexpected) promotion because there was a reorganistation project going on which I hopped in as some kind of leadership position. That was somewhat fun, but showed me its nothing I would want to do forever as main occupation. It yielded a new position a pay grade higher which I could also secure for myself (trough official application). I was not yet officially qualified for this, but could convince the HR people to allow me to apply with the promise of getting some further education; in reality I already did large parts of that job description, but the public sectors loves paper qualifications. I even got them to pay for the education program :)
Well, so I am now some kind of informal team leader without all the legal stuff. I still do plenty of technical work like before and *this* was like I envisioned it. If you read my initial posting, you can already see that I love technical IT stuff, especially software development. I knew that in my subconsciousness and it really paid off in life quality terms.
I reduced work hours a little for ~2hrs, but that already paid big in life quality dividends. The hours is about the additional pay from the rise, so effectively i earn the same as before for a little less work.
All in all it turned out pretty well, and the big lesson was to follow my (contemplated!) feelings.
They already told me what to choose, and it just was hard to acknowledge it.