Yes, I'm a big fan of optocouplers, and have been looking into adding schmidts to some of my own designs.
If you move away from ME compilers you will probably reach quite a few more AVR developers, ME stuff seems to be fairly umpopular on most AVR forums.
Of course nothing beats Arduino for popularity and huge user base who like to share. But I'm not sure how much performance hit you'd take running Arduino vs standard C.

Marvin