I'd like not to have an admin page for this, because that will cause alot of maintenance OR the functionality will be alot less flexible (now each page/post can have their own blocks).
However, I agree that the current plugin uses quite a dangerous scenario for the blocks. I think having an 'inactive blocks' widget where you can see the old content is a great idea (like inactive widgets). First thing on my list for this plugin, so I'll let you know.
I would also like to build in caches for the different templates so you will see the right blocks even though they can't be retrieved automatically at that specific moment (http://wordpress.org/support/topic/multiple-content-block-dissapeared-after-update?replies=30#post-3963813).
Thanks alot for your ideas and work on this!