You wrote:

    How many have people out ther come up this wonderful and unique
story or plot point, and later found out that, while for you it's new,
elsewhere it's been done to death?

Sadly, the only way to avoid this is to write in universes that are 
not "over-trafficked".  I've never written a RANMA fiction for this 
reason.  I had an idea for one, but I felt there couldn't possibly be 
any RANMA ideas I could think of that hadn't been written by 
*someone*, and I was right.

------RM