I have been pondering this question for a while. I think I would like to have some single file to hold all the parameterized layouts to avoid the explosion of cells for the typical analog layout. A reasonably good way to keep everything fairly clean is to create a subdirectory (call it, let's say, "primitives") and move all those paramterized layout cells there. Then either add the command "addpath primitives" to the .magicrc file, or else you can start magic, issue the command "addpath primitives", then read in the design, then do "writeall force" to have magic write out the files with the correct references to the subdirectory, after which you don't need the "addpath" command again.