the wiring, the paint, the neck, and some of the others will have a measureable impact on tone. By measureable, I mean that there is a difference, even though you probably don't notice. I tend to think of things like this in the analogy of olympic sports, like how every new innovation will shave off 1/10,000,000,000th of a second. It's a measureable differemce, but when its that close, the only ones who care are the guy buying the widget, and the guy making it. Everyone else just goes "hey, cool".
As far as Eric Johnson goes, Look for the song "Cliffs of Dover". Eric's what happens when you blend Joe Satriani and Steve Vai with Stevie Ray Vaughn and Jimi Hendrix. Phenomenal player from Austin TX. If you can find a clip of his performance on Austin City Limits, I highly reccomend it. If you want, let me know and I'll email you one.