No determinism
Speaking as a German, I think there are quite a few problematic aspects to your post, Jinx.
Germany today is the dominant power in Europe, despite, well the entire history of the twentieth century [...] This is for some very good reasons, due to its size, population, resources and an effective culture.
Right now, if Germany is the dominant power in Europe, it´s because its government can borrow massive amounts of money at good conditions and, consequently, lend massive amounts of money, too. Angela Merkel and her Chancellor of the Exchequer, Wolfgang Schäuble, pursue just the policy that the capitalist elites need and which they believe is the only sound one, the inevitable one. They combine this policy with feigned commitment to a unified Europe (allegedly continuing a post-WWII policy begun by Adenauer, who saw Western alignment as a way to re-integrate his pariah state with its horrible recent past into a political alliance) and the already mentioned financial power. Britain, where Cameron pursues the same economic policies, doesn`t show the same commitment to Europe. France and Italy don`t have the same credit on the financial markets. Why they don`t have this credit has less to do with Germany`s size, population, resources or culture, but rather with the cultural view of others on Germany: We´re expected to be good with money because we`re ascribed an "effective culture", as you put it; now whether that describes our culture well or not is quite a different question, but financial credibility is mostly a self-fulfilling prophecy (less trust = higher interest rates = higher risks at defaulting = less trust).
What I´d be really interested in is: Where exactly does this idea that Germany has an "effective culture" come from? In spite of the hyperinflation of 1923, the mismanagements in the GDR (if you blame communism for that, then don`t forget that Marx and Engels were Germans), not to mention the two wars.
My question is this - how inevitable was the unification of Germany? And what would have happened if it hadn't?
What does the unification have to do with Germany`s current power? Without the former GDR, Germany would still be the most populous member of the EU and its largest economy. Economically, it would fare much better (without the high costs of failed modernisation policies, infrastructural investments and welfare for largely unemployed workforces in the former GDR), and old Western Germany`s commitment to a unified Europe was even greater than that of post-1990 Germany.
Anyway. How inevitable was the unification of Germany, you ask?
At a very general level, not inevitable at all. The German-speaking world is still divided into Germany, Austria and parts of Switzerland. There is no intrinsic reason in itself why there couldn`t be four German-speaking states instead of three.
At a more concrete level, the unification between the FRG and the GDR in 1990 is harder to avoid. I can see two options:
1.) Either you go back to the 1940s and arrange for a different division of Germany, not splitting it into a capitalist US-aligned Western Germany and a communist Soviet-aligned Eastern Germany (of which they latter would be inclined to break down in the long run and become absorbed by the former, as it did IOTL), but rather, for example, into four, six or even more states (the size of its Czech, Swiss, Belgian or maybe even Luxemburgian neighbours), which would all be bound to neutrality and non-alignedness (like Austria). Breaking up Prussia into a (predominantly Catholic and left-leaning) Rheinland and a (predominantly Protestant and initially conservative) Northern Germany, making Berlin a free city, letting the Bavarians set up their independent state and lump the rest together in a "German Federation" of sorts could do the trick.
2.) Or you need somebody other than Mikhail Gorbachev in power in the USSR. As the GDR´s economy tottered and its population sought greener pastures, a country like the GDR only has three choices:
a) politically authoritarian economic reform, like in China
b) political and economic reform within a socialist framework, or
c) simply imitating the Western model.
With option c), there`s no reason for the GDR government not to want unification (because they don`t have to carry all the burden alone), and as unification has been the proclaimed aim of all Western German governments and parties post 1949 and, once the borders were opened, hundreds of thousands of GDR refugees poured across them to the West, I don`t see how the West could have denied that wish.
With option b), the mass migration would still take place, condemning the demographically anaemic New GDR experiment to failure and exerting pressure on the Western German government to "convince" their Eastern neighbours of letting go of their democratic socialist dreams and aligning to option c).
With the reformist Gorbachev in power in Moscow, option a) was not on the table.
So, if you want a PoD way past the 1940s that could have prevented German unification, you`d need somebody else in power in the USSR, some hard-liner or an authoritarian reformer like Deng Xiaoping. If they allowed, encouraged or helped Honecker (or Krenz) to crush the Monday demonstrations and keep the borders shut, starting market-oriented reforms but officially still flying the red flag, then the GDR could have developed into something that would not be absorbable by the Federal Republic.
(Of these two scenarios, I´d much rather live in version 1 than in version 2, though.)