Riding a shinkansen isn't like riding some old-time long-distance train in Europe or North America; it's basically just like riding in an airliner, but on the ground and without TSA and the seats have more legroom. It's all about speed and convenience, not luxury.
There are, however, some luxury trains in Japan on some routes. They're not bullet trains though, and usually meant more for sightseeing travel.
It might not actually be profitable, but it sure is sweet.
ICE trains run on the same lines used by slower services, and no train in Germany exceeds 300 km/h, with even that speed being attained only on quite small upgraded parts of the network.
The European rail network most similar to Shinkansen would be TGV.
While the high-speed tracks in Germany are indeed quite a bit of a patch-work, there are over 1000 km of track certified for >= 250 km/h (as of 2015; quite a number of more lines got finished since then, but I could not find the updated number that included them) and by now really rather long corridors are very high-speed. The route from Munich (south of Germany) to Berlin is now mostly covered with upgraded routes for example. I think the 4 hours for that route are quite competitive to Shinkansen times. The fastest Shinkansen route (from the listed operating speed the only one that actually operates at 320 km/h; all others only operate at 260-300 km/h) is the Tōhoku Shinkansen line, which takes 3 hours and 20 minutes for the same distance traveled.
I don’t think this is necessarily true. Gran class seats on a shinkansen are some of the fanciest I’ve seen. It’s not quite like a first class airliner, but I think that’s more related to the shorter journeys.
It would probably be more luxurious to put in private train compartments, which already exist on Japanese trains, but not on Shinkansen due to a capacity crunch.