I can answer this question as POI's are such a catch-22 for us.
All of these new Cityscapes are created with custom software that allows tens of thousands (or hundreds of thousands) of custom buildings that are accurately sized and placed, with little impact on frame rates. This is achieved by using shared texture sheets, low poly buildings and a unique way to compile scenery that allows over 500 objects to be compiled as a single object and rendered using a single draw call.
In contrast to this, you can have single detailed POI's that are created using tens of thousands of polygons that require many draw calls to render.
Because objects in the Cityscapes are viewed from a moving aircraft, as opposed to airport buildings where detail is more important, we refrain from creating any POI's whose details are going to really bog down performance. It is not out of the question to have a single POI that hurts performance more than 5,000 lower poly but accurately sized and placed buildings (those created by our software). Any POI's that have a lot of curved surfaces eat up polygons especially. This includes things like castles, churches and custom buildings.
In addition to the performance degredation, there is of course the extended development time needed to hand create a single POI (we are trying to keep the Cityscape costs down).
I hope this helps explain why, unlike detailed airport scenery packages, you will not find a lot of extremely detailed POI's in our Cityscapes. With that said, if there is a really iconic POI that can be rendered without a terrible performance hit, we are all for providing them.
The POI's that we did include in this scenery, in addition to those FSX/P3D library objects that were rescaled and positioned, we chosen because of their availability and mild performance hit.
PS-Looking at this list of objects, I agree that the WELA Hotel would be a good candidate for a POI due to the location in the flight path and importance. We could probably create a decent rendering of the object without too much of a performance hit.
These 3 objects however, Montjuïc Castle, Basilica del Tibidabo and Parque de Atracciones del Tibidabo would appear to be both difficult to develop efficiently.