Yes Gp, I believe that some of them needs to be larger, and others taller, to give you the appearance you´re looking for. But it will increase the final polly count.

Still, if you need some ideas for the greebles, not how to model them (I´m totally sure you already know how to do it

) , take a look and get some inspiration here:
Alternate Perspective Online. 3D Animation, Network Render Farm Services and Web Authoring .
You can always consider a mapped detail and bump maps, and still got the aspect you´re looking for. Take a look at this tut from Kier:
Space Environment Tutorial.