Interesting...
One way you could do it is to explode one of the block references. The explode method leaves the original in place. Now you have access to the sub entities and you could do what you want to them. Then use them to redefine the block. I'm not sure that this would be much faster though.
I haven't thought of that. This would get around the block editing commands. Might be worth a try..
Its is probably this (command "_.JOIN" "_ALL") that takes the time, if you have lots of items to join. May not be able to get around it.
Yeah, it seems to really slow down with more then 20000 objects or so. Not really surprising, I guess.
And I highly doubt that writing my own join function would be any faster.
Thanks for the help guys!