Is good enough really good enough?

Is JL audio components, stock speaker locations, and a w7 in the back good enough?

I'm building a 300zx. Going to be RHD, nice suede and leather interior the whole bit. Going for a nice, clean, daily driven type of build, For now.
But I want some good audio in it.
At first, we were thinking about going balls out. stripping it all the way down, sound proofing, custom speaker mounts, audio processor etc etc But I'm starting to think that it isn't gonna be worth it. Seems almost like the gap from "good enough" to "awesome" isn't very much in audible sound but huge in price tag.
Right now we're in the "paper build" part of it. Pricing it all out, getting a solid plan put together while the funding gets worked out. We don't want to sound like the average, wal mart bought, tossed together, sound system. We want better than that, but it doesn't need to be a competition level build either. With my limited knowledge of the audio industry, I don't really know where to draw the line as far as "good enough"

Is a stand alone audio processor really going to give that much better sound?
or can a decent head unit handle it?

Would the average person notice the difference between a door mounted component versus a custom kick panel install?

Any recommendations? components, subs, tweeters, amps, head units, processors, sound deadening, wiring, etc etc etc? tips, tricks, cheat codes?

hugely appreciated.