Thanks a lot for your reply, JH.
I have previously had the intended layout.view override working with both Graffiti 1.2 (by Telligent) and Graffiti 1.3 Alpha (first open source version), but with Graffiti 1.3 Beta 2 I just can't get it to work.
I am aware that the category link name must be used when naming view files (including the dashes) and I had already turned caching off for testing, so these are not the troublemakers.
I had a look at the Source Code history here in Codeplex today and I notice
Change Set 52527 saying "Prevented a CategoryName.view file from overriding the default post.view file for posts in that category"
However I don't know if this change also prevents a specific category layout.view file from overriding the normal layout-view file for posts within the specific category.
As mentioned in my initial post, I believe I initially received a special code-fix advice from Telligent in the old original Graffiti Forum, which is not available anymore, and I have not been able to locate posts describing similar issues.
The reason why I want different layout.view files is that my general layout.view file has a 2-column layout whereas my specific layout.view files have a 3-column layout which is also used for posts within the specific category.
Thanks for any further advice on how to get the override layout.view functionality to work.