I came across this post and wondered if there is a way to activate only a few of all of my installed plugins depending on the workspace I currently work in.
For example
Eclipse plugins are expected to start only as needed, in a lazy manner. I'm not saying that all behave exactly that way, but if you write your own plugin, you'll see this is how the technology works, your plugin gets called only as needed.
So in Eclipse, if you configure your starting Perspective (Java for me) to have only the Views you need, the plugins that are used for other views should not be started. To do this, take the view away and save your perspective (Windows - Save perspective as).
In addition, in Ganymede, in Windows - Preferences - General - Startup and Shutdown, there is a list of plugins that should be started on startup, so you can edit that list. I didn't try to see if this works per workspace though.