Filters are the ticket to achieving that.
Get the June 2010 Finescale modeler mag out, or get it in a back issue. I do an article on using filters in that one.
Applying a dirty filter to the top of the panels will work. You can also use chipping using a sponge or brushwork to add weathering as well.
And don't forget; you're modeling to make yourself happy, not necessarily anyone else. If you like your models and your results, don't freak yourself out because a master like Miguel critiques it. What fun would modeling be if everyone's models turned out the same?