I only use the vertex modeler if I absolutely have to.  I find I can create just about anything with the spline modeler, but yes.  To make things as mal;eable as possible, I do each subcomponent as a seperate object.  Like the individual frame elements of a window for instance; I then group them into a finished assembly module in the assembly room.  Then it is just a matter of assembling the various sub assemblies in the assembly room.  If you need to modify something, you can then just open up the objuect in the modeling room again if you need to make adjustments.  If you don't create a seperate master for multiple instances of the same object, this makes it very easy to modify all of the instance of an object by just modifying the master for it.  Just make sure you watch the amount of master shaders the program is creating whenever you copy or duplicate an object.  The program has a tendency to create a brand new copy of each shader for each copy of the master object, so you may want to go in and manually re-apply the shader for each copy you make of an object.  Sometimes I will create a completely seperate file for any sub assemblies which are overly complex.  This allows you to create the master sub assembly without haveing to deal with the other objects cluttering up the browsers etc.  Then just copy the new subassembly back into your main document, or save it into your My Objects folder (make sure to save the preview with it if you do this.)  The nice thing about saving it to my objects as well as just copying it to the main file is that if you ever need a sub assembly like this again, it is always there.  If you are an architect, this could save you a LOT of time.  Just create all of the sub assemblies into a folder, call it Elements or something, then create modules which can be simply put together to create the basic building you are working on.   Right now I am working on a Victorian era Seaside Hotel, and I am using this approach so that the modules I use can be reused by whoever purchases the model in my store to modify the hotel or create a brand new model using my modules if he or she needs to.  Having a seperate modeling and assembly is the main reason I use Carrara as opposed to 3DS, Cinema4D Lightwave etc.  I makes it a lot easier to design complex models without constantly having to change camera angles to see around and past other elements.