That final castle is looks almost like a cathedral, Rapunzel. Great stuff, you must have a massive stock of Steck parts to create these wonderful structures.
I'm trying to imagine how these would look if you were trying to use System-X. First off of course there'd be a lot of annoying empty holes on the outside, spoiling the overall look.
The roofs would be impossible I think, because Playmobil haven't provided enough roof parts yet (as far as I know), and there are no System-X round towers.
Hopefully these things will come in time, and in a few years System-X will offer the same degree of freedom to build custom designs.