How could i configure drush to be always affirmative and verbose in a drush.ini-file? Could I configure drush for non-interacive usage from bash-scripts to be always affirmative as I would pass the --yes and -v-option in /etc/drush/drush.ini? I'm aware that I could set a bash-alias and that I could set it in /etc/drush/drushrc.php. But for reasons of clarity I'd like to use the ini-style-configuration.
Drush will not read options from php.ini / drush.ini by default.  Your best option would be to use a bash alias, or set $options['yes'] = TRUE; in a drushrc.php file.

If you really really have to set an option in drush.ini, you could hack this functionality by writing a policy file.  It would look something like this:

function policy_init() {
  if (ini_get('drush_yes')) {
    drush_set_option('yes', TRUE);
    // Drush does not expect a globla option to change
    // at this time, so you need to re-call _drush_preflight_global_options().
    // This is not a public API, so the name may change, etc.
    _drush_preflight_global_options();
  }
}


The only motivation I can see for doing this is if you already have some fancy mechanism for selecting your php.ini based on context.  If you wanted to do that, then put policy.drush.inc in ~/.drush, or some other location where Drush searches for commandfiles.

I have not tested this; post a follow-up comment if you really want to do this and have trouble with it.