I firmly believe that any political party that works to represent it's constituency is relevant. I don't personally agree that a Catholic centered political party would represent any kind of large demographic, there are still Catholics and they should still have representation within a governing body to represent their interests.
All interests are relevant, though not all should be given much consideration.
Yes, I think that the Centre Party of Germany is still relevant today, because it is an important part of history. The Centre Party, largely Catholic, was most popular during the Weimar Republic. But to understand contemporary Germany and World War II, one needs to appreciate all of the political forces leading up to the war.
There are fewer Catholics and more Protestants in Germany today, so the traditional views of the Centre Party aren't nearly as relevant as before. The time for the Centre Party to be relevant was during World War II when members of the centrists should have stood up to Nazis more fervently.
I do not believe the Centre Party of Germany has truly been relevant since it disbanded when Hitler came to power. The Centre Party has over the years made numerous attempts to band with many of the smaller religious parties in order to gain strength. While these attempts have been slightly successful, the Centre Party continues to limp along with fewer members and vastly declining political clout.
The German Centre Party was created in 1870 and dismantled on 5 July 1933. After World War II it was re-founded buy many people who had followed the party had moved to another party. They were represented through 1957, but have only a small following currently and are not particularly relevant.