Our basic approach to MusicXML import is to focus on the semantic data represented in the files, rather than to focus on the layout information. We don’t currently import things like page size, staff size, margins, or other things defined in the appearance element. We import the coarse formatting information for things like slur, tuplet, and dynamics placement (e.g. above or below the staff), stem direction, and the like.
But both because the fine-grained layout information is difficult to interpret in MusicXML files (because different applications export it with different assumptions about what it means) and because we have spent so much time and energy on making Dorico’s default behaviours so sophisticated, we choose to use MusicXML as a repository for semantic musical data, such that essentially importing a MusicXML file is akin to having input that music from scratch yourself directly into Dorico.
If you have completely finished projects in other applications where you have spent time fine-tuning the layout of the score and the parts, and have made many edits to the graphical appearance of the score, I would not recommend bringing that project into Dorico with the expectation that you should be able to pick up where you left off without doing any of that work again. But if you have projects in progress for which you have not yet e.g. done any fine layout work, then that would be a good candidate to bring into Dorico to finish off.