I know when i first got my insight from the dealer i was amazed at how useless the rear wiper seemed with the stock 12" (or it could have been smaller!) blade.
The first "mod" (although it's not necessarily a mod in the true sense of the word) was to snap a 28" blade on that arm. If you haven't done this, go to walmart, buy a new wiper blade and snap it on. the 28" _barely_ fits but it clears almost all viewable area from the rear.
I am amazed as every insight I have seen on the road still has the dinky wiper blade which wipes only a small amount of area. you don't have to be blind!