^Why would they "put effort" into the car park side of the Klugheim sound barriers. What a colossal waste of money that would be. Disney have more money to play with yet there are plenty of examples of the rear sides of themed facades or show-buildings visible from outside parks.
Plus in Phantasialand's case should they ever be successful in acquiring the currently privately owned Mystery car park it would undoubtedly be used for expanding the park so they would built up something new in front of it. Same as with the "Vertical Garden Wall" in-between Klugheim and Chiapas there's an element of (potentially very) long term thinking ahead there.
This façade is undoubtedly being themed. It's the front piece and entrance of the hotel after all. And from the expansion negotiations process we know Berggeiststrasse cannot be removed or rerouted so it also fits into long term planning - this will always be visible.
Also its being themed as we can see. The scaffolding on the left section is Universal Rocks working on concrete theming including a large chimney feature (the framework for which can be seen in previous pictures). And the metal plates appear to be textured with visible rust/ageing marks - not plain bog standard sheets of metal like the car park wall.
As for the administration building being visible from inside the area. How do you know this, have you been inside? The large 4 storey hotel building that's been built in front has most likely has sorted that view out. Leaving the only remaining unblocked section the side beside the overbank and Hotel Tower 3 - presumably they aren't fully theming everything surrounding only to then leave that one obvious patch bare. A façade will definitely be coming here. If any other bit remains visible over any building or façade we really can't say or judge until its done...
Back to the topic of the potential pull through tests though. If a full test has been done recently its an interesting coincidence that Taron's pull through tests with a full clearance profile frame (although on a basic chassis, not with an actual, or more likely as was done with new Python at Efteling: part of an actual, train as Looopings claims with F.L.Y.) also took place in the short November off season. Taron's tests can be seen from 8.28 in this construction documentary.