Spacer Plugin - How to delete

Try right-clicking some empty space in the same menu or toolbar where your spacer was (actually still is). Find the option for "Explore" or "Open in Explorer" and click that. Find the file called "Spacer.tlbplugin" and delete it. Let us know if you have trouble doing this.

And yes, each instance of the spacer plugin takes up memory, even if it's set to 0. So having a large number of them would still take up memory, even if you can't see them.