Well, people write mixed code because they feel more comfortable with c++ and that's ok. If you feel more comfortable with c++ then that's an advantage, of course.
Some years ago, I had the same thing, but not any more because I feel absolutely comfy with c# now. After you make c# your own, there is no need for any mixed code, really. And if you are concerned about performance, then this is something that can be learned (as the techniques are different).
The thing is, if there is an advantage, it must be personal.
Tan Silliksaar milemarx.com