I presume part of the cookie must specify the SketchUp version - so users don't try to download components they cannot load.

I will be interested if there ideas can turn into a way to select and download components. What I would like to do it have a dialog which starts at a specific collection in the 3D Warehouse - such as this one - so users can download trees:

or else starts with a search, such as

IRender nXt Plants2.jpg

Thanks for answers.

We ended up with approach similar to one of described by TIG: we have a separate layer with known and recognizable name and store all our geometry there. Any operation gets required data (actually it's only box size) from that layer and thus the problem with losing references to our stuff is solved.

Of course problem with appearance of our geometry in saved modelы is still relevant, but it seems we can and will have to live with that (because after reopening the plugin catches existing geometry)...