This is a very valid point indeed. Thank you :)

Based on this:
http://sumtips.com/2011/01/move-rename-wordpress-wp-content.html

The fact that you can move both the wp-content folder *and* the plugins folder separately of each other, would it not rather make sense to make it one option, PLUGINSPATH, which is just the base of where the plugins are stored? 
wp-content could be at /wp-foo, but the plugins folder could be at /wp-bar. But we only care that the plugins are in /wp-bar, so I think there's only one option needed.