sorry, I am not an artist , but take a look at the idea:
http://soften.ktu.lt/~jurgpral/etc/xoops_block_admin.gif

now there is inconveniece: in order to see a block we apply
2 filters: block visibility on [module/page] and showing it to some [group]. And U have to keep jumping system->groups vs system->blocks (some people get confused (earlier, me also )

My proposal - centralize those two deals, and XOOPS will be one more step forward in simplicity of administration
My idea means the change of interface not the change of core. just some of sql-stuff from admin:groups would go to admin:blocks.
If tables are too big to fit in window, I think some js will help to deal with it (some hide/show of table parts or sth).

=== other stuff (not so important ;)
Well there's also group access to the module, but this is not directly the block issue. System->Groups could be left as it is for backward compatibility, though again I would like to be able to set rights of all groups just on one panel (in simple table manner), without jumping.

Personally, I'd love for all things related to modules such as blocks, permissions and preferences was collected in one place: Under each module.

Still keeping the system admin, if you have a lot to setup - but have panes like in Mambo under each module's preferences, where you set Preferences (if any) Block visibility and positioning/weight (if any) and permissions for that particular module and the module's blocks.

Your suggestion isn't bad and some more clarity in this area would be good.

ok,
for example, drupal has administration of
module acces permissions for all user_groups in one page
http://drupal.org/node/view/3931

I propose to have this idea
* incorporated in System->Blocks for blocks access,
* and made similar in System->Groups for module access