@kdarvell said:

The list of folders automatically presented consists of the first level of the structure on my drive and three "recently used" folders, these 3 never change.

not exactly what you're looking for but in response to that ^ part..

it sounds like you want more options in the save as dialog.. click the button:

Screen Shot 2014-10-28 at 12.37.37 AM.png

....
you'll get an expanded version with better access to all the drives/folders:

Screen Shot 2014-10-28 at 12.43.24 AM.png

further, you might want to consider using the tags feature of osx.. create a sketchup tag (or whatever) and just apply that when saving a file.. it doesn't really matter where it goes because you can just click on the sketchup tag in finder and see all of them (or move all of them etc..)