I'm sure this subject has been beat to a bloody pulp and I tried my best to search to see if this idea had been suggested in the past and didn't really find anything so I'm posting it.
What if there was an optional texture pack that could be downloaded separate from the client software. It would contain for example, 300 megs of standardized textures that anyone can use, I guess similar to what's found under the Library folder in your inventory, but on a much grander scale. This pack would contain a large variety of taxtures for different purposes, enough that if one chose to, you could build your sim using just these basic textures. And since they're already on your harddrive, they would be pre-cached, separate from the existing cache, so that you would never ever have to download them. I would think if a basic sim used many of the basic textures and just a handful of custom textures it would load that much faster. The textures could be in an uncompressed state to minimize CPU load uncompressing them.
Neverwinter Nights has something similar called the Community Content Pack which had a bunch of objects submitted by the community and packaged into one large bulk package. Then maps were created uses these objects in the pack which sped up loading time when playing someone's custom map. You already downloaded the content pack to your system, it didn't need to go fetch the objects.
Since it's separate from the client installation package, the client can be upgraded regulary and the content pack could be expanded whenever convenient. If you wanted to get started fast you wouldn't have to download the texture pack but then you'd have to download every single texture as you do now.
Anyway I know I new but it was an idea I had and probably others had in the past. I just couldn't find anything posted that sounded like this idea.