I can see some of what you're saying, at least with appearance mods based on the way things have been going with OEM design. I look at that as both a knock on the aftermarket and props to Ford. OEM's really stepped up their game since the '05 Mustang came out, and its a lot harder for the aftermarket to make something that looks nicer than OEM.
An example: I look at this aftermarket shifter bezel, which doesn't seem to flow very well with the rest of the interior, it stands out as aftermarket stick-on
And this one by Ford, which looks a lot sleeker and works with a nearly stock interior:
But that said, you, the modder, can come up with a grand design for your car to make an aftermarket part work for you (or pick the part that works for your design). Like this blocky bezel done with the brushed metal shift knob:
Its just as blocky as the first one, but because its got the shifter ball and the billet HVAC knobs to tie it in, it works.
What bugs me about these shifter bezels (as an example of aftermarket) is that Ford seems to be the only one that makes a total replacement part. How friggin expensive can it be to make one that snaps into place with a leather or imitation leather boot? A total replacement would look a lot better because they wouldn't have to make something that has to fit over the OEM boot. Its kind of like that for a lot of aftermarket parts, a lot of them don't seem to have the same OEM fittment.