Based on some advice I read, I have meticulously named all my plugin php files with my adopted plugin prefix, being 'wpsm-' in this case. All my class files have the additional 'class' qualifier, making their prefix 'wpsm-class-'.
Now, while doing some early morning housekeeping, trying to get zoned into serious coding, I realised that as long as all my php files stay in my plugin's folder, there is no reason to prefix them all, and removing the prefix actually improves readability. Further, if I place all my class files in a 'code' or 'class' folder, I don't need the additional 'class' prefix.
What do readers of this question suggest for my naming conventions, in the context I describe above?
 Professional WordPress Plugin Development:
"When building a custom plugin, it’s essential that you prefix everything with a unique prefix. This means all plugins files, function names, variable names, and everything included with your plugin."