You can get models off the net, some free some not. Generally they are high poly unless they have been made specifically low poly. The curved surfaces in objects like bathroom fittings are mostly produced by complex algorithms which are aimed at quite high resolution...hence the large no of polygons. Strangely, it takes more skill to build low poly curved objects.
I have searched the net quite extensively in the past. Here are some links. Will post more later.http://modelsbank.3dm3.com/cat17.htmhttp://blender-archi.tuxfamily.org/Models#Bathroom
A cycas-based repository would be great. I´m certainly willing to share whatever little I have collected and built. Any ideas about where too create it? There is Box.net which seems good. Or Drop.io
It´s not easy to get away from the triangulation thing. That´s just the way polygon modeling is done, especially for curved surfaces. Some formats support quads. The other option is nurbs modelling which uses 3d math equations to create the actual curved surfaces...ie no polygons. But Cycas doesn´t support nurbs at this stage and also most renderers first convert a nurbs model to poly before rendering.
So poly it has to be. Remember the poly structure is not seen in the shaded or rendered model. After a while you learn to see past it.
Also, hi poly is ok if you have a fast graphics card and one or two more spare seconds for rendering time.
dxf and 3ds are good robust universally used interchange methods. Not all 3ds models are welded...mostly they can be edited. Don´t know much about GTS.