@Zygmund – let's see what we can do here. You state:
"It's not possible to directly add a new element to a group and it's impossible to select/create groups into groups."
1. Adding directly a new element to a group:
Possible by using the Layers Panel: just drag another object inside that group as it is presented in the Layers Panel (chose the place *after* the bottom most object in the group). To get to the bottom most object, just expand the tiny triangles of the objects presented in the Layers Panel.
2. Select groups in groups
Possible by selecting the group from the Layers Panel
3. Create groups in groups
Not possible directly, but indirectly (you have to have already a group somewhere on the spread).
Priciply the same as in #1, but you first have to have a group, that you can drag inside a group. If this is done, drag all the objects you want to group inside the group of that group, remove the other objects that initially established the group or move them out. All possible with using the Layers Panel.
What also is helping: Name or rename objects in the Layers Panel.
(CS5 and above)
And yes, a feature request would be a start for make it easier to work with groups…
Uwe