Hi Andreas,
It is a valid request and indeed with heavy scenes having a simple display version of a complex block can greatly help with the speed. Not sure how soon we could expect this implemented in Rhino though, but the good news is what @Brenda suggests is actually a valid workflow, with a bit of scripting help.
In any case I assume for each of your complex blocks you need to define a simplified ‘imposter’ version of it anyway. So the way to go would be to create some rule in your block naming standards. For example: Tree_01 (main detailed blocks), Tree_01–light (light version of it) or even Tree_01–lightest (super simple version). It could be a prefix or suffix, depending on your scene organization.
If you keep it organized this way, you can use the script attached. It automatically replaces the corresponding named block instances (you can use method to add prefix, add suffix or replace – replace can be used to remove prefix or suffix if you use “” (just hit Enter) as the replacer string.
I use this workflow on regular basis and seems to be working fine with good speed benefits, Obviously it is up to you to create the needed block libraries in heavy/light versions and keep your models organized.
hth,
Jarek
DIG_ReplaceCorrespondingBlocks.rvb (2.0 KB)