I'd be surprised if this didn't greatly help you against dictionary attacks. I'm pretty sure 90% of cracking dictionaries don't even touch that range of UTF-8. Once you get out of dictionary range brute forcing a password is much, much harder...
...although now I'm wondering how long it would take as a map reduce job...
It would also be trivial to write a program to update the dictionaries to include the flipped / reversed / other silly unicode trick version of everything already in the dictionary.
I wouldn't assume that this would help against dictionary attacks for long, if at all now considering that people have been doing stuff like this pretty much since unicode got "mainstream" status.
Good point. It's all one and zeros to computers.