How to get all arguments passed to function (vs. optional only $args)
$PSBoundParameters gets you all the parameters that were "bound" along with the bound values in a hashtable, it doesn't get you the optional/extra arguments. That is what $args is for. AFAICT the only way to get what you want is to combine the two:
$allArgs = $PsBoundParameters.Values + $args
$args returns any undeclared parameters, not optional parameters. So just don't declare parameters.
In PowerShell v2, you can use $PSBoundParameters to get all parameters in a structured way.