Following @ragzzy 's answer I use
public static string Value(this IWebElement element, IJavaScriptExecutor javaScriptExecutor)
{
try
{
string value = javaScriptExecutor.ExecuteScript("return arguments[0].value", element) as string;
return value;
}
catch (Exception)
{
return null;
}
}
It works quite well and does not alter the DOM