I have a menu (Main menu). It's a superfish based menu that contains simple dropdown appearances. This menu doesn't have any Superfish style attached to it. It just uses the JQuery of this library and that's it; because of this reason I now need to attach arrows to these specific menu links that contain dropdows... Is there any simple module for this purpose and would you even recommend a modular solution in this case?
I would recommend that you use the settings of the Drupal Superfish menu itself. There is an option to use "Auto-arrows".
They can be further themed via CSS.
Superfish settings (in configure superfish block)
This is your site html source. That auto arrow element is there, but because it uses a white background-image you will not see it, so style it like you need it.