First, Turkey is an ally that is important right now due to the Syrian civil war, and the resulting stream of refugees, and the deal with them.
Second, Turks are by far the biggest immigrant group by nationality/descent (how do you say "türkischstämmisch" in English?), there was active campaigning in Germany plus rows about cancelled election rallies, and the whole debate caused deep divisions within the German-Turkish community. Much the same as in the Netherlands.
It's not a bit more power to the president. The changes are designed to hollow out the checks and balances between the three powers of state in favour of the president.
Human Rights Watch:
The Council of Europe's Venice Commission:
I haven't looked myself in detail into the changes, but those are the experts in this stuff.
I wouldn't trust anyone with that, whether they're Erdogan, a Kemalist, or a left-wing Kurd (let alone a Grey Wolf). But realistically, who will be elected as first president under that constitution, what with Erdogan now being president, the country still in a state of emergency and no free press?