You are correct in that most users find supermodules to be beyond their requirements, even the G.P.I.
As a result there is no great sea of supermodules to tap into. This is unfortunate.
Probably the best place to start is with your system's factory presets. The smaller ones can easily be made into useful supermodules. In particular, the Virtual Racks bank has a nice selection of small effects that are ideal supermodule candidates.