Cheers, Tim, thanks for doing that.
Just a couple of points regarding the library objects:
The windsock needs to be placed at a heading of zero, otherwise it won't show the correct wind direction. Objects which react to the wind direction sometimes don't work unless you have at least two onscreen, so if you find that your windsock doesn't seem to work, try adding another to the scenery. If it doesn't make sense to show another windsock, you might need to hide it in a building or something.
Bear in mind that some objects -- in particular hangars and buildings with 'human' sized features, such as doors -- shouldn't be scaled too much from the default size. Placing a house at 50% might suit the footprint you want to fill, but users will notice that the door is only suitable for hobbits.
Some objects are designed for bulk use, through an optimisation process which minimises drawcalls -- all of the vegetation/trees, and some of the buildings, so don't be afraid to go crazy with these, particularly the trees.
As Tim said, this is the recommended way to add library objects. It does everything that other placement tools do, and a lot of them are done better. Just a couple of gotchas:
Whisplacer isn't that clever when it comes to file extensions, so you need to actually add the extension to file names, it won't do it for you. So if you are saving your scenery as a BGL file, don't forget the .bgl extension.
I can't get 'Save As... BGL compiled scenery' to work, so instead I generally do a Manual Compile to go straight to BGL. I only save as XML if I need to edit the XML code.
Tim has already mentioned the fact that resized objects will appear at 100% when you place them, so getting the right size correct is a bit tricky. Within Whisplacer, the footprint will show correctly, so this can be used to fine-tune the size. For example, when placing a warehouse on a specific footprint, I first place some simple objects at the edges of the footprint, then resize the warehouse in Whisplacer until the placement boxes meet. Sounds, tricky, but once you try it you'll see the benefit.
Whisplacer gives an easy way to insert the XML tags such as 'NoShadow', and they all work well - except 'NoShadow', which is the most common one I need. To overcome this, I use 'NoFog' instead, then use search/replace in the resulting XML file to replace it with the NoShadow tag. You should do this as the final step, as reloading the scenery back into Whisplacer can remove all your tags.
Lastly, Whisplacer had no error checking when it comes to rotating objects using Shift and the mouse. You can rotate to less than zero degrees, or more than 360, and it will let you do that but will give a compile error. It is best to use the Edit box to change the heading, as trying to debug a file where you've rotated everything manually is not much fun.
Good luck, looking forward to seeing some airports appear.