I think the closest you can get to proxy/instanced objects in ArchiCAD is to use the simple/detailed 3D settings of most native ArchiCAD objects.
The PolyCount addon allows you to mass set these, but results may vary. You do need to remember to change the settings back and forth as you do the renders.
You can hide furniture details like handles, faucets and such with model view options, but not the 3D detail level that I can tell.
A whole different approach, that I sometimes use, is where I hotlink my entire ArchiCAD model of the building to a separate 3D presentation project where I add all the site work, people, trees etc etc so these do not clutter my bim model/technical drawing. It's a bit like how I use to work with Artlantis, export from ArchiCAD, add the 3d presentation stuff in Artlantis, except now it is a separate ArchiCAD file.
You could also make a special renovation filter for the 3d presentation models and set the objects to only show on that renovation filter. I use this a lot when I just add a bit of flavour site work that might be different for different cameras. What works in one camera composition, doesn't allways work in another.
Erwin Edel, Project Lead, Leloup Architecten
www.leloup.nlArchiCAD 9-26NED FULL
Windows 10 Pro
Adobe Design Premium CS5