For simplicity, every sentence should end with a full stop (period). Thus:

    How are you today?.

    This is important!.

Which clearly demonstrates that ! and ? can appear in the middle of a sentence, just as ; and , can:

   I want to call to your attention this very important!! point: always checks the return value of your system calls.

I do draw the line at introducing scoping operators though it would simplify the grammar.