Here's what happens at my location:
Blocks are inserted a number of ways.
Blockwerx, Toolbars, slide libraries and plain ol' DDInsert. The blocks aren't loaded into the templates or anything like that...well, the few that make up the border (Title block, rev block, etc.)
Layers are all set up in the templates, because if they weren't, it's very likely that people wouldn't know enough to create the right ones with the proper names and other settings. Should the layers happen to be purged out, I have a block contains a list of all standard layers and each layer name is ON that layer. It also contains the linetypes that we commonly use here. When the block is inserted into a purged drawing, it brings in all of the layers with it. It's almost like a 'layer recovery' block, I suppose.
Dimension Styles are all pre-loaded in the stanard border templates as well...
my 2¢...