I tried this 3 step approach but it DID NOT WORK - it basically adds any geometry associated to nodes/elements to the group in which nodes/elements are.
step1. Turn on all groups in the db then go to Meshing, Associate > Element > Solid, select all solid elements followed by all solid geometry and click Apply.
step2. Repeat the process for plate elements. Meshing, Associate > Element > Surface, select all shell elements followed by all surfaces and click Apply.
step3. Go to Utilities > Group > Group Extend + MPCs + Exclude , set Process=Geometry, Group Selection=Posted , click Apply.
Theoretically this should've grabbed all geometry but it did not work.
Your step 3 wouldn't be expected to work. The Group Extend tool in geometry mode will find geometry congruent with any existing geometry in the group; it doesn't look for geometry associated to mesh in the group. There doesn't seem to be a way currently to do that in an automated way. It can probably be done with some PCL.