WireWorld was used a lot baqck in old computer saves, I think underused elements are powdered quartz and powered void.
I think goo is pretty underated, and +1
I don't count hidden elements because they are, well, hidden.
You could have just made them circles :P
...and LOLZ and LOVE too....srry
I was considering putting EMP in there BTW.
I think EMP is also under used